Projection optical system and method for photolithography and exposure apparatus and method using same

ABSTRACT

A projection lens of a microlithographic projection exposure apparatus includes a final lens element and a terminating element having no overall refractive power that is positioned between, but spaced apart from, the final lens element and an image plane of the projection lens. The image plane is adjustably positioned such that a position of the image plane with respect to the final lens element is adjustable.

This is a Continuation of application Ser. No. 10/525,372 now U.S. Pat.No. 7,362,508, which is the U.S. National Stage of InternationalApplication No. PCT/JP2003/010665 filed Aug. 22, 2003. The disclosure ofeach of the prior applications is hereby incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present invention relates to projection optical systems such assystems for photolithography.

The present invention also relates to an exposure apparatus and exposingmethods. The invention is applicable to a high-resolution projectionoptical system suitable for an exposure apparatus used whenmanufacturing semiconductor elements or liquid crystal display elementsthrough a photolithographic process.

BACKGROUND ART

In the following the term “anastigmat” means an optical element or groupof optical elements adapted to reduce astigmatism and/or aberrationsincluding spherical aberration. See, e.g. Naumann/Schröder, Bauelementeder Optik, Carl Hauser Verlag München Wien, 6^(th) ed., 1992, pp.382-383 for a discussion of the term anastigmat. The term “Mangin mirrorarrangement” means an optical device comprising a concave mirror and atleast one negative powered lens proximal to the concave mirror whereinthe concave mirror need not be in contact with the negative poweredlens.

In the lithographic process for manufacturing semiconductor elements orthe like, it is the usual practice to use a projection exposureapparatus for exposing a pattern image of a mask (or a reticle) onto awafer (or a glass plate or the like) coated with photoresist via aprojection optical system. Along with improvement of the degree ofintegration of semiconductor elements, the demand for achievableresolution of a projection optical system of the projection exposureapparatus is steadily increasing.

As a result, in order to satisfy the resolution requirement of theprojection optical system, it is necessary to reduce the wavelength λ ofthe illuminating light (exposing light) and/or increase the numericalaperture NA of the projection optical system. More specifically, theresolution of a projection optical system is expressed by k·λ/NA (wherek is a process coefficient). When assuming the refractive index of amedium (usually a gas such as air) between the projection optical systemand the image field to be n, and the maximum incident angle to be θ,then, the numerical aperture NA on the image side can be expressed asn·sin θ.

Historically, resolution in microlithography has been improved either byincreasing the numerical aperture (NA), or by reducing the wavelength ofillumination light, or a combination of the two.

When it is tried to increase the numerical aperture by adopting a largermedium incident angle θ, the incident angle on the image plane and theoutgoing angle from the projection optical system become larger, leadingto an increase in reflection loss on the optical plane. It is impossibleto ensure a large and effective numerical aperture on the image side. Atechnique is known for increasing the numerical aperture NA by fillingan optical path between the projection optical system and the imagefield with a medium such as a liquid having a high refractive index. WO99/49504 discloses a projection exposure method that irradiates exposurebeams on a mask and transfers the pattern of said mask onto a substratevia a projection optical system, wherein when said substrate is movedalong a predetermined direction, a predetermined liquid is passed alongthe direction of the motion of said substrate so as to fill the spacebetween the end of the optical element on said substrate side of saidprojection optical system and the surface of said substrate, anddiscloses a projection exposure apparatus that irradiates exposure beamson a mask and transfers the pattern of said mask onto a substrate via aprojection optical system, comprising a substrate stage that moves whileholding said substrate, a liquid supply device that supplies apredetermined liquid along a predetermined direction via pipes forsupply so as to fill the space between the end of the optical element ofsaid substrate side of said projection optical system and the surface ofsaid substrate, and a liquid recovery device that recovers said liquidfrom the surface of said substrate via said supply pipes and pipes fordischarge arranged so as to sandwich the irradiation area of saidexposure beams in said predetermined direction, and wherein when saidsubstrate stage is driven to move said substrate along saidpredetermined direction, supply and recovery of said liquid isperformed. The direction of the flow of the liquid may be changedaccording to the direction of the motion of the substrate. Theprojection exposure apparatus may be provided with a second pair ofsupply pipes and discharge pipes arranged at the location where saidpair of supply pipes and discharge pipes would be if they wereessentially rotated by 180°. The projection exposure apparatus may alsocomprise a liquid recovery device that recovers liquid supplied tobetween said projection optical system and said substrate.

U.S. Pat. No. 4,509,852 teaches using a photolithographic projectionapparatus a mask having a pattern is imaged on a photosensitive layercoating a semiconductor substrate by a projection lens. To improve theresolving capability and to obviate adverse effects, e.g. standing wavesand inhomogeneous exposure, the space between the substrate and theadjacent boundary face of a projection lens is filled during exposurewith a transparent liquid having the same refractive index as thephotosensitive layer.

However, a concrete proposal has not as yet been made regarding aconfiguration which ensures a large and effective image-side numericalaperture.

The theoretical resolution improvement of liquid-immersion is well knownin microscopy, where oil-immersion dioptric objectives have for manyyears been designed with NAs greater than 1.0, but covering only a verysmall field of 0.5 mm or less. See, for example: “Modern OpticalEngineering”, by Warren Smith, Third Edition, page 450, published bySPIE Press and McGraw Hill.

Liquid immersion applied to microlithography has also been proposed formany years, but has been slow to be adopted in production, no doubtbecause of practical difficulties. However, the theoretical advantagesbecome stronger as “dry” projection lens NAs approach the theoreticallimit of 1.0. These advantages have been described in, for example: “Thek3 coefficient in nonparaxial λ/NA scaling equations for resolution,depth of focus, and immersion lithography” by Burn J. Lin published inJM3 1(1) 7-12 April 2002.

More recent investigations into the practical issues of liquid immersionfor lithography have also become more optimistic, for example:“Resolution enhancement of 157 nm lithography by liquid immersion” by M:Switkes and M. Rothschild, published in JM3 1(3) 225-228 October 2002.However, neither of these papers addresses the issues of optical design.

Early papers proposing liquid immersion lithography include: “Opticalprojection lithography using lenses with numerical apertures greaterthan unity” by H. Kawata, J. M. Carter, A. Yen and H. I. Smith,published in Microelectronic, Eng. 9, 31 (1989); “Fabrication of 0.2 μmfine patterns using optical projection lithography with an oil immersionlens” by H. Kawata, I. Matsumura, H. Yoshida and K. Murata, published inJapan, Journal of Applied Physics, Part 131, 4174˜1992; “⅛ μm opticallithography” by G. Owen, R. F. W. Pease, D. A. Markle, A. Grenville, R.L. Hsieh, R. von Bunau and N. I. Maluf, in the Journal of Vacuum ScienceTechnology, B10-6, 3032˜1992; and “Immersion lithography at 157 nm” byM. Switkes and M. Rothschild, in the Journal of Vacuum ScienceTechnology, B19-6, 2353˜2001.

The recent Switkes paper is the most significant, in that it proposesthe use of water as the immersion liquid for ArF (or KrF) laser light,perfluoropolyethers for F₂ laser light, and starts to address thepractical issues involved with a scanning wafer stage.

Another recent paper has started to address optical design issues forthe relatively wide field of views used in lithography, partiallydisclosing liquid immersion dioptric microlithographic projection lensdesigns with NAs of greater than 1.0: “Development of dioptricprojection lenses for DUV lithography” [4832-18] by Ulrich Wilhelm,Rostalski Hans-Juergen, Hudyma Russell M, published in SPIE Vol. 4832IODC June 2002.

US 2001/0040722 A1 describes a catadioptric design which uses a V-foldmirror and two intermediate images. However, this is a small-fieldsystem (<1 mm), specifically intended for optical inspection, and thereis no indication that the design could be applied to the much largerfield sizes and extremely small residual aberrations and distortionrequired for microlithography.

“High numerical aperture lithographic imagery at the Brewster angle” byTimothy A. Brunner et al, in JM3 1(3) 188-196, October 2002, describesthe fundamental disadvantages in terms of image quality, as the NAapproaches 1.0 in a “dry” projection lens. These relate to vectorimaging degradation that is made worse by Fresnel reflection losses atthe resist interface, which more strongly reflects and loses thepolarization orientation that would have given the better image qualityinside the photoresist. This occurs most strongly at Brewster's angle,which corresponds to a NA of about 0.85.

We have investigated liquid immersion dioptric designs, and have foundthat for a NA of 1.0 and 26 mm field size the largest lens diametersneed to be of the order of 330 mm, which is on the limit of availablehigh quality fused silica, and beyond the limit for calcium fluoride.There is also a reduction in spectral bandwidth, in the same way thatthere is for “dry” dioptric lenses as the NA increases. A reduction infield size and an increase in reduction ratio above 4× would help theseissues, but would make the “wet” lithography tools incompatible withcurrent “dry” systems.

Known “dry” catadioptric designs have relatively small lens diametersand chromatic aberrations. However, they cannot be converted to liquidimmersion only by adding a liquid to the space between the last elementand the wafer. This would introduce a large amount of sphericalaberration, which has to be compensated elsewhere in the design. Also,in simply adding a liquid, the NA does not increase, since thedefinition of NA already includes the refractive index.

Immersing the wafer in liquid is a necessary, but not sufficient,condition for being able to increase the NA up to the theoreticalmaximum equal to the liquid refractive index (˜1.4), rather than 1.0 ina “dry” system. For a constant magnification, paraxial geometricaloptics theory (in particular, the Lagrange invariant) dictates that anincrease of NA at the wafer has to be accompanied by a correspondingincrease in NA all the way through the projection lens system. Thisresults in an increase in lens diameters, and optical surface steepness,defined by the ratio D/R, where D is the clear aperture diameter and Ris the radius of curvature. At the same time, chromatic and high-orderaberrations increase rapidly with NA.

It is therefore not obvious to one skilled in the art of optical designthat the NA of a “dry” projection lens can be increased in the ratio ofthe refractive index of the immersion liquid, without both animpractical increase in the lens size and complexity, as well as anunacceptable increase in residual aberrations.

Textbooks on optical design (e.g. Warren Smith, Modern OpticalEngineering Third Edition, page 449-450, published by SPIE Press andMcGraw Hill) describe the historical microscope immersion objective witha hyper-hemispherical convex surface (clear diameter/radius of curvaturebeyond hemispherical, where D/R=2) on the last element, opposite theplane surface in contact with the immersion liquid. Classically, thissurface is designed to be either aplanatic, or close to the aplanaticcondition. At the aplanatic condition there is zero sphericalaberration, coma and astigmatism, and the marginal ray convergence angleis greater inside the lens element than before it by the ratio of theglass refractive index. Being close to this aplanatic conditionminimizes spherical aberration and coma, and is a simple way ofincreasing NA, which is useful for a small field microscope objective,or systems such as the prior art US Patent Application US 2001/0040722.

For microlithography, which requires small aberrations over a muchlarger field size, such an aplanatic surface would give rise tohigher-order aberration variations across the field, including obliquespherical aberration and coma. It is common practice to use, instead, aconvex surface on this last element that is not at the aplanaticcondition, but rather at or near the so-called concentric, ormonocentric condition. In the concentric situation the marginal rayconvergence angle inside the last element is identical to that incidentupon it. Again there is zero spherical aberration and coma, but moreimportantly for a wide-field system there is zero sagittal obliquespherical aberration. See, for example, J. Dyson, JOSA, volume 49(7), p.713 (July 1959), or, “Monocentric telescopes for microlithography” by C.G. Wynne, Optical Engineering, Vol. 26 No. 4, 1987.

J. G. Baker, The Catadioptric Refractor, The Astronomical Journal, Vol.59, pp. 74-84 (1955) discusses pros and cons of a telescope which isbased on a concept suggested by Schupmann (L. Schupmann, DieMedial-Fernrohre, Eine neue Konstruktion für gro

e astronomische Instrumente, Teubner, Leipzig, 1899).

SUMMARY OF THE INVENTION

An object of the invention is to provide a projection optical systemwhich permits achievement of a large and effective image-side numericalaperture by providing a medium having a high refractive index in anoptical path to the image field and inhibiting satisfactorily thereflection loss on the optical surface. Another object of the inventionis to provide an exposure apparatus and an exposing method which have alarge and effective image-side numerical aperture and enable to transferand expose a fine pattern at a high accuracy via a projection opticalsystem having a high resolution.

According to a first aspect of the invention there is provided aprojection optical system for projecting an image of a first plane ontoa second plane comprising: a boundary lens; and at least one layer ofimmersion medium between the boundary lens and the second plane; saidboundary lens having a first plane side optical surface shaped such thatfor light projected onto the second plane through the boundary lens themarginal ray convergence angle prior to incidence is larger than themarginal ray convergence angle within said boundary lens.

According to a second aspect of the invention there is provided aprojection optical system for projecting an image of a first plane to asecond plane comprising: an optical system; a boundary lens; and atleast one layer of immersion medium between said boundary lens and saidsecond plane; wherein light from the first plane is transmitted throughthe optical system, and output with a predetermined marginal rayconvergence angle; and said boundary lens is positioned to receive saidlight output from the optical system, and adapted such that for lightprojected onto the second plane through the boundary lens the marginalray convergence angle prior to incidence is larger than the marginal rayconvergence angle within said boundary lens.

The optical system (which means the optical system of the opticalprojection system, where the former is included in an optical projectionsystem) may further comprise at least one positive powered lens elementproximal to said boundary lens, and having an aspheric optical surface.

Alternatively, the optical system may further comprise a first positivepowered lens element proximal to said boundary lens, and having at leastone aspheric optical surface, and a second positive powered lens elementbetween the first positive powered lens element and said boundary lens,and having at least one aspheric optical surface.

The optical system may be one in which the first positive powered lenselement has an axial thickness greater than 26.1 mm and less than 28.9mm, and a first plane side surface with an axial radius of curvaturegreater than 103 mm and less than 114 mm, the second positive poweredlens element has an axial thickness greater than 26.5 mm and less than29.3 mm, and a first plane side surface with an axial radius ofcurvature greater than 83.2 mm and less than 91.9 mm, and the boundarylens has an axial thickness greater than 41.6 mm and less than 46.0 mm,and a first plane side surface with an axial radius of curvature greaterthan 56.9 mm and less than 62.9 mm.

Instead, the optical system may comprise a first positive powered lenselement proximal to said boundary lens, and having at least one asphericoptical surface, and a second positive powered lens element between thefirst positive powered lens element and said boundary lens, and havingat least one aspheric optical surface, wherein the first positivepowered lens element has an axial thickness greater than 27.22 mm andless than 27.77 mm, and a first plane side surface with an axial radiusof curvature greater than 107.6 mm and less than 109.8 mm, the secondpositive powered lens element has an axial thickness greater than 27.63mm and less than 28.19 mm, and a first plane side surface with an axialradius of curvature greater than 86.67 mm and less than 88.42 mm, andthe boundary lens has an axial thickness greater than 43.37 mm and lessthan 44.25 mm, and a first plane side surface with an axial radius ofcurvature greater than 59.27 mm and less than 60.46 mm.

Any of the optical systems defined above may include a double-Gaussanastigmat arranged to reduce spherical aberration including a thirdpositive powered lens element, a first negative powered lens element, asecond negative powered lens element, and a fourth positive powered lenselement.

In this optical system the third positive powered lens element has anaxial thickness greater than 43.9 mm and less than 48.5 mm, and a firstplane side surface with an axial radius of curvature greater than 128 mmand less than 141 mm, the first negative powered lens element has anaxial thickness greater than 13.1 mm and less than 11.9 mm, and a firstplane side surface with an axial radius of curvature greater than 1540mm and less than 1710 mm, the second negative powered lens element hasan axial thickness greater than 11.9 mm and less than 13.1 mm, and afirst plane side surface with an axial radius of curvature greater than184 mm and less than 204 mm, and the fourth positive powered lenselement has an axial thickness greater than 30.6 mm and less than 33.9mm, and a second plane side surface with an axial radius of curvaturegreater than 189 mm and less than 209 mm.

As an alternative to the optical system described in the precedingparagraph, the optical system may be one in which the third positivepowered lens element has an axial thickness greater than 45.71 mm andless than 46.63 mm, and a first plane side surface with an axial radiusof curvature greater than 133.3 mm and less than 136.0 mm, the firstnegative powered lens element has an axial thickness greater than 12.38mm and less than 12.63 mm, and a first plane side surface with an axialradius of curvature greater than 1608 mm and less than 1641 mm, thesecond negative powered lens element has an axial thickness greater than12.38 mm and less than 12.63 mm, and a first plane side surface with anaxial radius of curvature greater than 191.9 mm and less than 195.8 mm,and the fourth positive powered lens element has an axial thicknessgreater than 31.91 mm and less than 32.56 mm, and a second plane sidesurface with an axial radius of curvature greater than 197.4 mm and lessthan 201.3 mm.

The optical system in any form as described above may comprise acatadioptric anastigmat comprising a concave mirror and at least onenegative powered Schupmann lens.

In this optical system the catadioptric anastigmat can comprise twonegative powered Schupmann lenses.

Any of the above optical systems may be adapted for use with ultravioletlight.

The optical system may comprise a set of optical elements substantiallyhaving the parameters as set out in Tables 1 and 2.

The optical system may comprise a set of optical elements havingparameters substantially based on those in Tables 1 and 2, but adjustedto be re-optimised for a particular operating optical wavelength

According to a third aspect of the invention there is provided a methodof projecting an image of a first plane onto a second plane includingthe steps of passing light having a first marginal ray convergence angleto a boundary lens, passing light having a second marginal rayconvergence angle though the boundary lens, and passing light from saidboundary lens through a layer of immersion liquid to the second plane,wherein the first marginal ray convergence angle is greater than thesecond marginal ray convergence angle.

The method may include the step of passing light through at least onepositive powered lens element proximal to said boundary lens, and havingan aspheric optical surface.

Alternatively, the method may include the steps of passing light througha first positive powered lens element proximal to said boundary lens,and having at least one aspheric optical surface, and passing lightthrough a second positive powered lens element between the firstpositive powered lens element and said boundary lens, and having atleast one aspheric optical surface. This method may include the steps ofpassing light through a first positive powered lens element proximal tosaid boundary lens, and having at least one aspheric optical surface,passing light through a second positive powered lens element between thefirst positive powered lens element and said boundary lens, and havingat least one aspheric optical surface, passing light through the firstpositive powered lens element having an axial thickness greater than26.1 mm and less than 28.9 mm, and a first plane side surface with anaxial radius of curvature greater than 103 mm and less than 114 mm,passing light through the second positive powered lens element having anaxial thickness greater than 26.5 mm and less than 29.3 mm, and a firstplane side surface with an axial radius of curvature greater than 83.2mm and less than 91.9 mm, and passing light through the boundary lenshaving an axial thickness greater than 41.6 mm and less than 46.0 mm,and a first plane side surface with an axial radius of curvature greaterthan 56.9 mm and less than 62.9 mm. Alternatively the method may includethe steps of passing light through a first positive powered lens elementproximal to said boundary lens, and having at least one aspheric opticalsurface, passing light through a second positive powered lens elementbetween the first positive powered lens element and said boundary lens,and having at least one aspheric optical surface, passing light throughthe first positive powered lens element having an axial thicknessgreater than 27.22 mm and less than 27.77 mm, and a first plane sidesurface with an axial radius of curvature greater than 107.6 mm and lessthan 109.8 mm, passing light through the second positive powered lenselement having an axial thickness greater than 27.63 mm and less than28.19 mm, and a first plane side surface with an axial radius ofcurvature greater than 86.67 mm and less than 88.42 mm, and passinglight through the boundary lens having an axial thickness greater than43.37 mm and less than 44.25 mm, and a first plane side surface with anaxial radius of curvature greater than 59.27 mm and less than 60.46 mm.

The methods as defined above may include the step of passing lightthrough a double-Gauss anastigmat arranged to reduce sphericalaberration including a third positive powered lens element, a firstnegative powered lens element, a second negative powered lens element,and a fourth positive powered lens element. Such methods may include thestep of passing light through a double-Gauss anastigmat arranged toreduce spherical aberration including a third positive powered lenselement having an axial thickness greater than 43.9 mm and less than48.5 mm, and an object side surface with an axial radius of curvaturegreater than 128 mm and less than 141 mm, a first negative powered lenselement having an axial thickness greater than 13.1 mm and less than11.9 mm, and a first plane side surface with an axial radius ofcurvature greater than 1540 mm and less than 1710 mm, a second negativepowered lens element having an axial thickness greater than 13.1 mm andless than 11.9 mm, and a first plane side surface with an axial radiusof curvature greater than 184 mm and less than 204 mm, and a fourthpositive powered lens element has having axial thickness greater than30.6 mm and less than 33.9 mm, and a second plane side surface with anaxial radius of curvature greater than 189 mm and less than 209 mm.Instead the method may have the step of passing light through adouble-Gauss anastigmat arranged to reduce spherical aberrationincluding a third positive powered lens element having an axialthickness greater than 45.71 mm and less than 46.63 mm, and a firstplane side surface with an axial radius of curvature greater than 133.3mm and less than 136.0 mm, a first negative powered lens element havingan axial thickness greater than 12.38 mm and less than 12.63 mm, and afirst plane side surface with an axial radius of curvature greater than1608 mm and less than 1641 mm, a second negative powered lens elementhas an axial thickness greater than 12.38 mm and less than 12.63 mm, anda first plane side surface with an axial radius of curvature greaterthan 191.9 mm and less than 195.8 mm, and a fourth positive powered lenselement has an axial thickness greater than 31.91 mm and less than 32.56mm, and a second plane side surface with an axial radius of curvaturegreater than 197.4 mm and less than 201.3 mm.

Any of the methods as defined above according to the third aspect of theinvention may include the step of passing light through a catadioptricanastigmat comprising a concave mirror and at least one negative poweredSchupmann lens, and this method may have the step of passing lightthrough a catadioptric anastigmat comprising a concave mirror and twonegative powered Schupmann lenses.

The light as used in the methods as defined above may be a beam ofultraviolet light.

The method may include the step of passing light through a set ofoptical elements having substantially the optical properties as set outin Tables 1 and 2.

The method may have the step of passing light through a set of opticalelements substantially having optical properties based on those set outin Tables 1 and 2 but re-optimized for a particular operatingwavelength.

The method may include the step of passing light through a set ofoptical elements substantially having optical properties based on thoseset out in Tables 1 and 2 but re-optimized for a particular operatingwavelength and a particular immersion layer thickness.

According to a fourth aspect of the present invention there is provideda projection optical system for projecting an image of a first planeonto a second plane, comprising:

an optical path having a plurality of lenses including a boundary lenswhich is arranged at a position closest to the second plane, wherein thefirst plane side surface of the boundary lens has a positive refractivepower, and for an atmosphere in said optical path having a refractiveindex of 1, the optical path between the boundary lens and the secondplane is filled with a medium having a refractive index larger than 1.1.

According to a preferred embodiment of the fourth aspect, the projectionoptical system satisfies the condition as expressed by:0.012<Cb·D/NA<0.475where, Cb represents the curvature of a face of the boundary lens on thefirst plane side; D represents the distance between an optical axis andthe outermost point of an effective image forming area, and NArepresents the numerical aperture on the second plane side. It isdesirable that, in the projection optical system, at least one opticalmember having substantially no refractive power is detachably arrangedin the optical path between the boundary lens and the second plane; andthe optical path between the boundary lens and the optical member, andthe optical path between the optical member and the second plane arefilled with said medium. In this case, the optical member havingsubstantially no refractive power has an adjustable posture. Thecondition |P·D|<1.0×10⁻⁴ should preferably be satisfied, where, Prepresents the refractive power of the optical member havingsubstantially no refractive power; and D represents the distance betweenthe optical axis and the outermost point of the effective image formingarea.

It is desirable that the projection optical system is areflecting/refracting optical system comprising at least one concavereflector and a refractive optical member. In this case, the projectionoptical system should preferably have an effective image forming areaeccentric relative to the optical axis, and at least one intermediateimage should preferably be formed in the optical path of the projectionoptical system. It is desirable that the projection optical systemcomprises: a first image forming optical system for forming a firstintermediate image on the first plane; a second image forming opticalsystem, having at least one concave reflector, for forming a secondintermediate image on the basis of the first intermediate image; and athird image forming optical system for forming a final image on thesecond plane on the basis of the flux from the second intermediateimage; wherein a first deflecting mirror is arranged in the optical pathbetween the first image forming optical system and the second imageforming optical system; a second deflecting mirror is arranged in anoptical path between the second image forming optical system and thethird image forming optical system; and the optical axis of the firstimage forming optical system is aligned with the optical axis of thethird image forming optical system.

The numerical aperture on the first plane side should preferably be 0.22or larger. The light quantity loss occurring upon passing through themedium should preferably be 50% or lower.

A fifth aspect of the present invention provides an exposure apparatuscomprising an illuminating system for illuminating a mask set on thefirst plane, and a projection optical system for forming an image of apattern formed on the mask on a photosensitive substrate set on thesecond plane.

A sixth aspect of the present invention provides an exposing methodcomprising the steps of illuminating a mask set on the first plane, andprojecting and exposing a pattern image formed on the mask on aphotosensitive substrate set on the second plane via the projectionoptical system.

A seventh aspect of the present invention provides an exposure apparatusfor transferring a pattern formed on a mask onto a photosensitivesubstrate comprising an illuminating optical system for illuminating aprescribed illumination area on the mask, and a projection opticalsystem for projecting a reduced image of the pattern into an exposurearea on the photosensitive substrate; wherein the projection opticalsystem is a reflection/refraction optical system comprising a boundarylens arranged at a position the closest to the photosensitive substrateside; the exposure area is eccentric from the optical axis of thereflection/refraction-type projection optical system; and when theatmosphere in an optical path of the projection optical system isassumed to have a refractive index of 1, an optical path between theboundary lens and the second face is filled with a medium having arefractive index larger than 1.1.

In some aspects of the projection optical system of the presentinvention, the image-side numerical aperture NA is increased byproviding a medium having a refractive index larger than 1.1 in anoptical path between the boundary lens arranged at a position theclosest to the image side (second plane side). The paper “ResolutionEnhancement of 157-nm Lithography by Liquid Immersion” published by M.Switkes and M. Rothchild in JM3 1(3), pp 225-228, October 2002identifies Florinat (perfluoropolyethers: commercial name by Three-MCompany, the United States) and deionized water as media having aprescribed transmissivity for a beam having a wavelength λ of 200 nm orless.

The projection optical system of the present invention may reduce thereflection loss on the optical surface, and finally ensure a large andeffective image-side numerical aperture by imparting positive refractionpower to the face of the boundary lens on the object side (first planeside). In the present invention, as described below, it is possible toachieve a projection optical system which enables to keep a large andeffective image-side numerical aperture by inhibiting the reflectionloss on the optical surface to a satisfactory level by providing amedium having a high refractive index in the optical path to the imagefield.

The following conditional formula (1) should preferably be satisfied. Inthis formula, Cb represents a curvature of the face of the boundary lensfacing the object; D, the distance between the optical axis and theoutermost point of the effective image forming area (in the case of anexposure apparatus, the distance between the optical axis and theoutermost point of the effective exposure area); NA, the numericalaperture on the image side (the second plane side). The terms “effectiveimage forming area” and “effective exposure area” mean an image formingarea and an exposure area, of which the aberrations have beensufficiently corrected.0.012<Cb·D/NA<0.475  (1)

A value exceeding the upper limit of the conditional formula (1) is notdesirable because correction of aberration cannot sufficiently beaccomplished over the entire effective image forming area (effectiveexposure area). A value lower than the lower limit of the conditionalformula (1) is not desirable because a sufficient reduction ofreflection loss on the optical surface cannot be achieved, leading to asmaller effective numerical aperture, and finally to a poorerresolution. In order to further reduce the reflection loss and anabsorption loss and obtain a high resolution over the entire effectiveimage forming area (effective exposure area), it is desirable to set anupper limit of the conditional formula (1) of 0.400, and a lower limitof 0.015.

As described above, a fluorine-based inert liquid such as Florinat or aliquid such as deionized water is used as a medium having a highrefractive index provided between the boundary lens between the boundarylens and the image field so as to make it possible to ensure a requiredtransmissivity (to inhibit a light quantity loss). In the case of anexposure apparatus, the liquid may suffer from contamination by thephotoresist coated onto a substrate such as a wafer. The contaminatedliquid may stain the image-side optical surface of the boundary lens,causing a decrease in transmissivity of the boundary lens and theliquid.

Therefore, it is desirable to detachably arrange an optical member(usually an optical member having substantially no refracting power)such as a parallel flat sheet in an optical path between the boundarylens and the image field. In the manufacturing process of a projectionoptical system, it is possible to adjust the Petzval sum and correctcurvature of the image plane by selectively replacing the optical memberprovided between the boundary lens and the image field.

It is furthermore desirable to adopt a configuration so as to permitadjustment of the orientation of the optical member having substantiallyno refractive power. In this case, asymmetrical aberration caused bylens eccentricity can be corrected by tilting the optical memberrelative to the optical axis. The optical member having substantially norefractive power should preferably satisfy the following conditionalformula (2):|P·D|<1.0×10⁻⁴  (2)

In the conditional formula (2), P represents the refractive power of anoptical member having substantially no refractive power (=1/focallength); and D, the distance between the optical axis and the outermostpoint of the effective image forming area (in the case of an exposureapparatus, the distance between the optical axis and the outermost pointof the effective exposure area). A value higher than the upper limit ofthe conditional formula (2) is not desirable because it leads to largechanges in the other aberrations upon correcting the asymmetricalaberration by tilting the optical member.

The projection optical system should preferably comprise areflection/refraction optical system having at least one concavereflector and a refractive optical member (lens component). Thisconfiguration permits achievement of a projection optical system havinga large effective image forming area (effective exposure area) and alarge image-side numerical aperture NA. In general, in the case of arefractive-type projection optical system comprising a refractiveoptical member alone, it is necessary to bring the Petzval sum as closeto 0 as possible by alternately arranging a positive lens group and anegative lens group on the object side (near the object surface) of asmaller numerical aperture, in order to correct the field curvature.

However, in an optical system having a large image-side numericalaperture, the numerical aperture is large also on the object side. It istherefore difficult to satisfactorily correct spherical aberration orcoma over the entire effective image forming area (effective exposurearea) while correcting the Petzval sum to 0. In this case, by alteringthe reduction magnification from 1:4 to a reduction at highermagnification such as 1:5 or 1:6, correction of the Petzval sum can beachieved because the object-side numerical aperture becomes smaller.However, when trying to ensure a wider effective exposure area in anexposure apparatus, this practice encounters the difficulty of requiringan excessively large mask.

In a reflection/refraction-type projection optical system having atleast one concave reflector and a refractive optical system, incontrast, the concave reflector makes a contribution to the Petzval sumsimilar to that of a negative lens while having a positive refractivepower. Correction of the Petzval sum can be easily made through acombination of the concave reflector and the positive lens. As a result,it is possible to achieve a projection optical system having a largeimage-side numerical aperture and a wide effective image forming area(effective exposure area) by a combination of a configuration of thereflection/refraction optical system and a configuration of aliquid-immersion optical system in which a liquid (medium) having a highrefractive index is provided in the optical path from the image plane.

In the reflection/refraction optical system, a problem is how toseparate a beam directed toward the concave reflector from a return beamreflected from the concave reflector. In a projection optical systemhaving a large image-side numerical aperture, increase in the effectivediameter of the optical element (adoption of larger optical elements) isinevitable. Therefore, in a reflection/refraction optical system using aprism-type beam splitter having a transmission reflection surface, thedifficulty is encountered that it is difficult to manufacture alarger-sized prism-type beam splitter. The projection optical systemshould preferably have a configuration in which the system has aneffective image forming area eccentric from the optical axis, and atleast one intermediate image is formed in the optical path. In thisconfiguration, it is possible to easily separate the beam directedtoward the concave reflector from the return beam reflected from theconcave reflector by arranging a flat reflector for separating theoptical paths near the forming position of the intermediate image.

Furthermore, the configuration should preferably be such that theprojection optical system comprises a first image forming optical systemwhich forms a first intermediate image of the object surface (the firstplane); a second image forming optical system which has at lease oneconcave reflector and forms a second intermediate image on the basis ofthe flux from the first intermediate image; and a third image formingoptical system which forms a final image on an image field (the secondplane) on the basis of the flux from the second intermediate image; afirst deflection mirror is arranged in an optical path between the firstimage forming optical system and the second image forming opticalsystem; a second deflection mirror is arranged in an optical pathbetween the second image forming optical system and the third imageforming optical system; and the optical axis of the first image formingoptical system agrees with the optical axis of the third image formingoptical system. In this configuration, even in an optical system havinga large image-side numerical aperture, it is possible to easily separatethe beam directed toward the concave reflector from the beam reflectedby the concave reflector to return. It is also possible to relativelyeasily accomplish assembly or adjustment of optical systems since thefirst image forming optical system and the third image forming opticalsystem are coaxial.

As described above, a projection optical system conducting sizereduction at a high magnification such as 1:5 or 1:6 is unfavorable inthat application to an exposure apparatus results in a mask larger insize. Therefore, the object-side numerical aperture should preferably be0.22 or larger for obtaining a high resolution at an appropriatereduction magnification. In addition, the light quantity loss causedupon passing through a medium present between the boundary lens and theimage field should preferably be 50% or lower. When this configurationrequirement is not satisfied, light absorbed by the medium generatesheat, and image formation tends to deteriorate under the effect of thefluctuation of the refractive index in the medium.

For a better understanding of the invention, and to show how the samemay be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of a catadioptric “dry” projection systemfor comparison purposes;

FIG. 2 shows an illustration of a catadioptric liquid immersionprojection lens system according to a first embodiment of the presentinvention;

FIG. 3 shows an illustration of the last optical elements in the opticalpath of FIG. 2;

FIG. 4 shows an illustration of the boundary lens, the immersion liquidlayer and the image plane;

FIG. 5 shows an illustration of the marginal ray path passing into thelast lens element according to the first embodiment of the presentinvention;

FIG. 6 shows an illustration of the marginal ray path passing throughthe last lens element into the immersion liquid layer according to thefirst embodiment of the present invention;

FIG. 7 schematically illustrates the configuration of exposure apparatusincorporating the present invention;

FIG. 8 illustrates the positional relationship between a rectangulareffective exposure area formed on a wafer and a reference optical axisin second and third embodiments of the invention;

FIG. 9 illustrates the positional relationship between a rectangulareffective exposure area formed on a wafer and a reference optical axisin a fourth embodiment;

FIG. 10 schematically illustrates the configuration of a boundary lensand a wafer in the second to fourth embodiments;

FIG. 11 illustrates the lens configuration of the projection opticalsystem of the second embodiment of the invention;

FIG. 12 illustrates lateral aberration in the second embodiment;

FIG. 13 illustrates the lens configuration of the projection opticalsystem of the third embodiment of the invention;

FIG. 14 illustrates the lateral aberration in the third embodiment ofthe invention;

FIG. 15 illustrates the lens configuration of the projection opticalsystem of the fourth embodiment of the invention;

FIG. 16 illustrates the lateral aberration in the fourth embodiment;

FIG. 17 is a flowchart of the technique used when obtaining asemiconductor device as a microdevice;

FIG. 18 is a flowchart of the technique used when obtaining a liquidcrystal display device as a microdevice;

FIG. 19 illustrates the lens configuration of a fifth embodiment of theinvention; and

FIG. 20 illustrates graphs showing various aberrations of the fifthembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is an illustration of a catadioptric “dry” projection system forcomparison purposes, which was disclosed in EP1191378A1. This “dry”projection system includes a first set of field lens elements L11 toL13, a meniscus anastigmat L14 to L17 which aids in correctingaberrations, and a positive powered set of lens elements L18 to L20,which together comprise a first field lens group G1, a beam splittingmeans FM (1, 2), a Mangin mirror arrangement G2 including two Schupmannlenses L21, L22 and a concave mirror CM which provides an aberrationcorrecting function. The system also includes a positive powered set oflens elements L31 to L33, a negative lens element L34, a positivepowered set of lens elements L35 and L39, a negative powered anastigmatL40 which corrects aberrations, and a positive powered lens element L41which together comprise a second field lens group G3. Light is passedfrom a reticle R through the first field lens group G1, then through thebeam splitter FM (1, 2) to Mangin mirror arrangement G2, and finallythrough the beam splitter FM (1, 2) and the second field lens group G3.By this arrangement an image may be conveyed from the reticle R to awafer W with negative magnification so as to controllably expose aphotoresist on the wafer.

FIGS. 2 and 3 and Tables 1 and 2 show a detailed embodiment of theinvention. Light from the object plane OP passes through a plane windowE201, a first positive powered group of field lens elements E202 andE203, an anastigmat E204 to E208, adapted to reduce sphericalaberration, a second positive powered group of field lens elements E209to E211, a beam splitter E212 and E218, a catadioptric anastigmatincluding two Schupmann lenses E213 and E214 and a concave mirror E215,the beam splitter E212 and E218 for a second time, a third positivepowered group of field lens elements E219 to E221, a double-Gaussanastigmat E222 to E225 arranged to reduce spherical aberration, afourth positive powered group of field lens elements E226 to E232, aboundary lens E233, a layer of immersion liquid IL, and to an imageplane IP.

The fourth positive powered group of field lens elements includes afirst positive powered lens element E231, and a second positive poweredlens element E232. The double-Gauss anastigmat includes a third positivelens element E222, a first negative powered lens element E223, a secondnegative powered lens element E224, and a fourth positive powered lenselement E225.

In Tables 1 and 2 preferred values of the radius of curvature and theaxial distances between optical surfaces of optical elements E210 toE233 are given. As those skilled in the art will appreciate, workablesystems may be designed in which all the parameters given in Tables 1and 2 may be allowed to vary from the specific values given by plus orminus 1 percent, and even up to plus or minus 5 percent with appropriateadaptation. For example when operating at 157 nm this would give forsurface S263 a radius of curvature greater than 56.9 mm and less than62.9 mm, or more preferably greater than 59.27 mm and less than 60.46mm, or most preferably 59.8643 mm. The values for the radius ofcurvatures of the curved surfaces of the optical elements E202 to E233and for the thicknesses and separations of the optical elements E202 toE211, E213 to E215, and E219 to E233 will of course change if theoperating wavelength is changed.

Accordingly, the thicknesses of lens elements E222 to E225 and E231 toE233, and the radius of curvatures of optical surfaces S240, S242, S244,S247, S259, S261 and S263 may have values as follows:

the first positive powered lens element E231 has an axial thicknessgreater than 26.1 mm and less than 28.9 mm, and an object side surfaceS259 with an axial radius of curvature greater than 103 mm and less than114 mm;

the second positive powered lens element E232 has an axial thicknessgreater than 26.5 mm and less than 29.3 mm, and an object side surfaceS261 with an axial radius of curvature greater than 83.2 mm and lessthan 91.9 mm;

the boundary lens E233 has an axial thickness greater than 41.6 mm andless than 46.0 mm, and an object side surface S263 with an axial radiusof curvature greater than 56.9 mm and less than 62.9 mm;

the third positive powered lens element E222 has an axial thicknessgreater than 43.9 mm and less than 48.5 mm, and an object side surfaceS240 with an axial radius of curvature greater than 128 mm and less than141 mm;

the first negative powered lens element E223 has an axial thicknessgreater than 11.9 mm and less than 13.1 mm, and an object side surfaceS242 with an axial radius of curvature greater than 1540 mm and lessthan 1710 mm;

the second negative powered lens element E224 has an axial thicknessgreater than 11.9 mm and less than 13.1 mm, and an object side surfaceS244 with an axial radius of curvature greater than 184 mm and less than204 mm; and

the fourth positive powered lens element E225 has an axial thicknessgreater than 30.6 mm and less than 33.9 mm, and an image side surfaceS247 with an axial radius of curvature greater than 189 mm and less than209 mm.

More preferably, the ranges of values for the parameters of the opticalprojection system are within a narrower range of plus or minus 1% of thetabulated finite values.

Accordingly, the thicknesses of lens elements E222 to E225 and E231 toE233, and the radius of curvatures of optical surfaces S240, S242, S244,S247, S259, S261 and S263 may preferably have values as follows whenoperating at a wavelength of 157 nm:

the first positive powered lens element E231 has an axial thicknessgreater than 27.22 mm and less than 27.77 mm, and an object side surfaceS259 with an axial radius of curvature greater than 107.6 mm and lessthan 109.8 mm;

the second positive powered lens element E232 has an axial thicknessgreater than 27.63 mm and less than 28.19 mm, and an object side surfaceS261 with an axial radius of curvature greater than 86.67 mm and lessthan 88.42 mm;

the boundary lens E233 has an axial thickness greater than 43.37 mm andless than 44.25 mm, and an object side surface S263 with an axial radiusof curvature greater than 59.27 mm and less than 60.46 mm;

the third positive powered lens element E222 has an axial thicknessgreater than 45.71 mm and less than 46.63 mm, and an object side surfaceS240 with an axial radius of curvature greater than 133.3 mm and lessthan 136.0 mm;

the first negative powered lens element E223 has an axial thicknessgreater than 12.38 mm and less than 12.63 mm, and an object side surfaceS242 with an axial radius of curvature greater than 1608 mm and lessthan 1641 mm;

the second negative powered lens element E224 has an axial thicknessgreater than 12.38 mm and less than 12.63 mm, and an object side surfaceS244 with an axial radius of curvature greater than 191.9 mm and lessthan 195.8 mm; and

the fourth positive powered lens element E225 has an axial thicknessgreater than 31.91 mm and less than 32.56 mm, and an image side surfaceS247 with an axial radius of curvature greater than 197.4 mm and lessthan 201.3 mm.

Even more preferably, the values of the radius of curvature of thesurfaces of the optical elements E201 to E233, and the thicknesses ofthe optical elements E201 to E233, have values according to Tables 1 and2.

An important feature is the presence of a liquid (other than glass)between the image side surfaces S264 of the boundary lens 233 and theimage plane IP, both of which may be plane (infinite radius ofcurvature) as illustrated in FIG. 4. It should be noted that liquidsother than water, such as perfluoropolyether, may be used in someembodiments and that the use of the term “liquid” is meant to includeany fluid medium other than glass, having a refractive indexsubstantially greater than 1. Suitable liquids include water, (which maybe de-ionized and/or degassed) and perfluoropolyethers.

This embodiment of the invention provides improved resolution comparedwith the dry microlithographic projection system of FIG. 1, in which thewafer is immersed in a gas. The wafer is immersed in liquid, whichreduces the speed and wavelength of light incident on the photoresist bya factor of about 1.4, without changing the wavelength of the lightsource. It thereby allows numerical apertures (NA) significantly greaterthan 1.0, by avoiding the total internal reflection of light that wouldhave occurred at the last lens surface if the wafer had been immersed ina gas of refractive index close to 1.0.

The illustrated embodiment provides a specific “wet” catadioptricoptical design at NA 1.2, a factor of about 1.4 times higher than “dry”designs at NA 0.85 such as FIG. 1. This disclosed catadioptric designalso avoids some of the practical limitations of prior art dioptric“dry” immersion optical designs.

In this system, the theoretical advantages of liquid immersion arerealized by means of a catadioptric large-field deep ultravioletmicrolithographic projection optical design, whose NA is increasedbeyond the theoretical limit in air of 1.0, without the lens diametersor surface curvatures increasing beyond practical fabrication limits,and also without a reduction in field size or spectral bandwidth oflight source that would occur with prior art dioptric designs. The “wet”catadioptric NA 1.2 design has a track length (reticle-wafer distance)comparable to a “dry” catadioptric NA 0.85 design, and the sameinstantaneous wafer field size of 26×5 mm and a relatively smallincrease in lens diameters, which minimizes the changes required in thelithography scanner tool body design, while allowing the same scannedfields to be covered over the wafer.

A catadioptric design is preferred (although it is not essential)because it does not require large separation of negative and positivepowered lens elements for field curvature correction. Instead, the fieldis flattened by means of a concave positive powered mirror (element E215in FIG. 2 and Tables 1 and 2). Negative powered lens elements close tothis mirror (so-called Schupmann lenses, elements E213 and E214 in FIG.2 and Tables 1 and 2) provide further field curvature correction andsufficient achromatization for the NA to be increased above 1.0 withoutthe need for a second type of refracting material or a reduction inspectral bandwidth. This allows the design to be optimized for existing0.4 pm bandwidth line-narrowed ArF excimer lasers, using only fusedsilica lens elements, no calcium fluoride elements, and deionized waterof about 1 mm thickness as the immersion medium (IL in FIG. 2 and Tables1 and 2).

It would be straightforward to re-optimize the disclosed design for usewith a line-narrowed KrF laser. The design concept may also be appliedto an F₂ excimer laser, using only calcium fluoride lens elements withfor example a 0.1 mm thickness of perfluoropolyether immersion liquidlayer.

Many types of prior art “dry” catadioptric designs have been designedand published. However, this invention is most closely related to, butnot limited to, what may be described as the “V-type” catadioptricoptical design form, which uses V-shaped fold mirrors between twointermediate images. This form has the advantage of relatively smalllens diameters and a mechanical package similar to a dioptric lens. Itshould however be noted that alternatives exist to the V-shaped foldmirror, such as a splitter cube which has an equivalent effect.

In order to operate effectively with liquid immersion between the lastlens element surface and the wafer, this last optical surface shouldpreferably be a plane surface (surface S264 in FIGS. 2 and 4 and Tables1 and 2). This facilitates the liquid dynamics during wafer scanning,minimizes the possibility of bubble formation within the liquid, andminimizes sensitivity to magnification changes with liquid refractiveindex and dispersion (lateral color), since for a telecentric system inwafer space the principal rays enter the liquid at zero angle ofincidence.

In a classical liquid immersion microscope objective, the refractiveindex difference between the last lens element and liquid introducesspherical aberration, which is minimized by using the least possiblethickness of liquid and finding a liquid whose refractive index matchesas closely as possible that of the lens element. In the deep-UVmicrolithography situation, the thickness of the liquid is chosen forother reasons, such as optical transmission, as well as liquid dynamicsand mechanical considerations during wafer scanning and stepping. Thisdesign is not constrained by the choice of liquid thickness orrefractive index. Currently, a liquid thickness of 1 mm is assumed, butthe optical design may easily be re-optimized for a different thicknessor liquid refractive index. Again this is facilitated by having a planelast lens surface next to the liquid, when the spherical aberration isconstant across a large field size, and can be easily corrected at apupil plane in the system by means of at least one aspheric surface.

In this invention, neither the aplanatic nor concentric conditions areused in the last element, i.e., boundary lens, next to the wafer(surface S263 on element. E233, FIGS. 2 and 4). In this case, themarginal ray convergence angle is slightly smaller inside element 233than it was prior to entering it (as seen in FIGS. 5 and 6). Thisfeature has three advantages:

a. The D/R (clear diameter/radius of curvature) of this surface can beconstrained to be <1.5, which is within normal optical polishingtechniques for large, high quality, optical elements.

b. The resulting spherical aberration and coma may easily be correctedin other elements in the system, including several aspherical surfaces,which is advantageous in the correction of high-order aberrations thatchange rapidly across the wide field used in microlithography, such asoblique spherical aberration, coma, astigmatism and distortion. Thisstrategy is particularly effective in a long, complex system with twointermediate images, such as the V-type catadioptric design.c. There is no focused ghost image on the wafer surface, as would occurwith an exactly concentric surface.

Classical microscope objectives also employ at least one element beforethe last one that has a combination of aplanatic and concentricsurfaces. The preferred embodiment of the invention employs, instead, atleast two positive meniscus elements before the last one (elements E231and E232 in FIGS. 2 and 3 and Tables 1 and 2) whose surfaces are neitherexactly concentric nor aplanatic, so as to avoid both extreme curvaturesand extreme angles of incidence near or beyond the critical angle.

At least one of these surfaces may be aspheric, so as to perform similaraberration correction functions to those which in lower NA “dry” designsmay be achieved with air spaces between adjacent elements (e.g. the airspace between elements E230 and E231 in FIG. 2).

The relatively high optical power in the last three positive elementsminimizes the size increase of lens elements required in the rest of thesystem as the “dry” NA of 0.85 in designs such as FIG. 1 is increased toa “wet” NA of 1.2. This is very advantageous because the lenses wouldotherwise be larger than can be readily made with existing technology,and would thus be exceptionally expensive. The relatively high power ofthe last three elements also allows a pupil (aperture stop) positioncloser to the wafer than is typical in “dry” designs, e.g. FIG. 1.

A common feature of known catadioptric “dry” lithography projectionsystems is a negative powered element between the pupil and wafer. Thisfeature, which is used to correct aberrations has the disadvantage thatin a “wet” catadioptric optical projection system the main positivepowered lenses would have to be larger than otherwise. The newarrangement in the present application has the advantage that it doesnot require such a negative powered lens and this further minimizes thelens diameter of the main positive powered lenses, and also the lengthof the optical path. The aberration correction of a negative lenselement in “dry” designs (e.g. element L38 in FIG. 1) is performed,instead, by an aspheric surface close to the pupil.

The negative powered lens group, elements E222 to E225 in FIG. 2, is adouble-Gauss anastigmat arranged to reduce spherical aberration. Itcontributes to field curvature and lateral color correction in theoverall design, while minimizing higher-order coma and oblique sphericalaberration that would otherwise be larger at NA 1.2 than they were in“dry” designs at NA 0.85 (FIG. 1). This feature provides the advantageof allowing a wider field of view than would otherwise be possible at NA1.2.

As illustrated in FIGS. 5 and 6, it can be seen that the angle L of themarginal ray of the light cone projected to the boundary lens E233decreases on passing into the boundary lens E233.

FIG. 5 and FIG. 6 illustrate one embodiment, where it can be seen thatthe geometric focus F of the marginal rays L, prior to entering theboundary lens E233, is located between the two optical surfaces S263 andS564 of the boundary lens, and is also between the centre of curvatureCC of the boundary lens and the optical surface S263 of the boundarylens.

As also can be seen from FIG. 6, as the refractive index of the boundarylens E233 may typically not be equal to, and practically would be higherthan, the refractive index of the layer of immersion liquid IL, theangle S of the marginal ray may increase on passing from the boundarylens E233 to the immersion liquid layer before impinging on the imageplane IP.

It should be noted that the terms “object plane”, “image plane”, “pupilplane”, and “plane mirror” are not limited to being plane surfaces, orplane mathematical surfaces, but may also be curved physical ormathematical surfaces. It should also be noted that the illustrations inFIGS. 1 to 6 are not to scale, and that the beam splitter E212, E218 maybe a single element having two optical paths there through.

The aspheric surfaces A(1) to A12) in Table 1 are defined by equation(3):

$\begin{matrix}{Z = {\frac{({CURV})Y^{2}}{1 + \left( {1 - {\left( {1 + K} \right)({CURV})^{2}Y^{2}}} \right)^{1/2}} + {(A)Y^{4}} + {(B)Y^{6}} + {(C)Y^{8}} + {(D)Y^{10}} + {(E)Y^{12}} + {(F)Y^{14}} + {(G)Y^{16}} + {H(Y)}^{18} + {(J)Y^{20}}}} & (3)\end{matrix}$CURV is the inverse value of the apex radius of curvature, and thevalues CURV (or Curv), A, B, C, D, E, F, G, H, and J are tabulated inTable 2.

In Table 1, the sign of the radius indicates the direction of curvature,CC indicates a concave surface and CX indicates a convex surface. In theembodiment of table 1 the largest diameter of any of the lens elementsE202 to E211, E213 to 217, E219 to E228 and E229 to E233 is only 242.8mm for the positive lens element 227.

TABLE 1 Axial distance Radius of Curvature to next surface Ele- BackBack ment Front Front E201 Infinity Infinity 8.0000 1.0000 E202 296.2214CX −960.8207 CX 29.0933 1.0000 E203 29.3195 CX 219.1233 CC 31.540269.4729 E204 105.2542 CX 433.274 A(1) 30.2818 1.1583 E205 77.5810 CX85.0063 CC 35.9523 30.5076 E206 −101.0777 CC −109.0575 CX 50.000022.2382 E207 −86.9124 CC −277.5585 CX 17.0119 14.1315 E208 −313.0101 CC−121.4285 CX 47.1365 1.0000 E209 244.5825 A(2) −150.1716 CX 43.87161.0000 E210 287.8659 CX −1006.7736 CX 33.3703 3.9387 E211 232.1539 CX3443.7633 A(3) 26.1499 64.9981 E212 Infinity −248.6029 E213 99.3337 A(4)760.1855 CX −12.5000 −41.6713 E214 112.9332 CC 210.0532 CX −12.5000−23.5805 E215 150.9146 CC 23.5805 E216 210.0532 CX 112.9332 CC 12.500041.6713 E217 760.1855 CX 99.3337 A(5) 12.5000 248.6029 E218 Infinity−64.0489 E219 3037.9516 CC 252.1281 CX −26.2012 −1.0000 E220 −422.2688CX 878.8560 CX −28.0789 −1.0000 E221 −197.8858 CX −1895.1173 CC −36.9167−1.0000 E222 −134.6900 CX 221.3134 A(6) −46.1691 −18.4179 E223−1624.3296 CX 89.3372 A(7) −12.5000 −44.5981 E224 193.8597 CC 211.4093A(8) −12.5000 −14.8193 E225 −1550.8977 CX 199.3485 CX −32.2367 −85.9268E226 1142.6351 A(9) 305.6765 CX −26.7479 −1.0002 E227 −341.9216 CX−5217.2118 CC −30.8753 −1.0000 E228 −274.1211 CX 3414.1345 A(10)−33.1045 −9.8682 AS Infinity 5.3722 E229 −337.4484 CX −6051.4400 CC−40.2177 −1.0007 E230 −286.9832 CX −47776.7480 CC −29.3234 −1.0000 E231−108.7000 CX 152.1155 A(11) −27.4984 −1.0000 E232 −87.5448 CX 167.7647A(12) −27.9141 −1.0000 E233 −59.8643 CX Infinity −43.8105 IL InfinityInfinity −1.0000

TABLE 2 K A B C D Aspheric Curv E F G H J A (1) 0.00230801 0.0000001.35800E−07 4.43804E−13 5.17522E−16 −2.13416E−20 1.24264E−23 0.00000E+000.00000E+00 0.00000E+00 0.00000E+00 A (2) −0.00408861 0.000000−2.93564E−09 3.96730E−13 −3.34166E−17 −3.22241E−22 5.62462E−26−1.64835E−30 0.00000E+00 0.00000E+00 0.00000E+00 A (3) 0.000290380.000000 2.58800E−08 −1.30225E−14   −1.33600E−17 7.99491E−22−2.36540E−26 4.15511E−31 0.00000E+00 0.00000E+00 0.00000E+00 A (4)0.01006708 0.000000 −7.39601E−08 −3.15605E−12   −2.13807E−16−1.63643E−20 −2.27561E−26 −3.78485E−28 0.00000E+00 0.00000E+000.00000E+00 A (5) 0.01006708 0.000000 −7.39601E−08 −3.15605E−12  −2.13807E−16 −1.63643E−20 −2.27561E−26 −3.78485E−28 0.00000E+000.00000E+00 0.00000E+00 A (6) −0.00451848 0.000000 4.41668E−09−5.79647E−13   −2.25277E−17 6.73716E−22 −1.21801E−25 −1.34613E−300.00000E+00 0.00000E+00 0.00000E+00 A (7) −0.01119354 0.000000−6.93411E−08 −3.30971E−12   −3.11788E−16 −2.65850E−20 −2.48878E−24−1.79947E−28 0.00000E+00 0.00000E+00 0.00000E+00 A (8) −0.004730160.000000 −4.72629E−08 6.08755E−12 −1.63469E−16 −2.65475E−20 1.16802E−24−3.23662E−29 0.00000E+00 0.00000E+00 0.00000E+00 A (9) 0.000875170.000000 1.10141E−08 −5.01692E−13   −2.00493E−17 −8.25872E−223.68761E−26 2.41555E−31 0.00000E+00 0.00000E+00 0.00000E+00 A (10)−0.00029290 0.000000 −6.20015E−09 −1.26050E−13   −3.59314E−171.65781E−21 −3.84229E−26 2.58938E−31 0.00000E+00 0.00000E+00 0.00000E+00A (11) −0.00657395 0.000000 3.58357E−08 −7.83628E−12   7.69481E−16−7.68364E−20 9.31381E−25 5.59854E−28 0.00000E+00 0.00000E+00 0.00000E+00A (12) −0.00596073 0.000000 −1.91466E−07 4.589321E−12  1.26164E−154.61975E−19 −6.00362E−23 −8.48073E−28 0.00000E+00 0.00000E+000.00000E+00

FIG. 7 schematically illustrates the configuration of an exposureapparatus incorporating the present invention. In FIG. 7, a Z-axis isset in parallel with a reference optical axis AX of a projection opticalsystem PL; a Y-axis is set in parallel with the paper plane of FIG. 1,within a plane perpendicular to the reference axis AX; and an X-axis isset perpendicularly to the paper plane of FIG. 1.

The exposure apparatus shown in FIG. 7 has an ArF excimer laser source(oscillation center wavelength: 193.306 nm; used in the second andfourth embodiments) or an F₂ laser source (oscillation centerwavelength: 157.631 nm; used in the third embodiment) as a light source100 for supplying illuminating light of ultraviolet range. The lightemitted from the light source 100 superposingly illuminates a reticle Rhaving a prescribed pattern formed thereon via an illuminating opticalsystem IL. An optical path between the light source 100 and theilluminating optical system IL is sealed with a casing (not shown), andthe space from the light source 100 to an optical member the closest tothe reticle in the illuminating optical system IL is substituted by aninert gas such as helium or nitrogen which is a gas having a lowabsorption rate of the exposure light, or kept in substantially a vacuumstate.

The reticle R is held in parallel with an XY plane on the reticle stagevia a reticle holder RH. A pattern to be transferred has been formed onthe reticle R. A rectangular (slit-shaped) pattern area having a longerside in the X-direction in the entire pattern area and a shorter side inthe Y-direction in the entire pattern area is illuminated. The reticlestage RS is two-dimensionally movable along the reticle surface (i.e.,the X-Y plate) under the effect of a driving system not shown. Thepositional coordinates are measured by a interferometer RIF using areticle moving mirror RM, and positionally controlled.

Light from the pattern formed on the reticle R forms a reticle patternimage on a wafer W serving as a photosensitive substrate via aprojection optical system PL. The wafer W is held in parallel with theXY plane on the wafer stage WS via a wafer holder table WT. Tocorrespond to the rectangular illuminating area on the reticle R, apattern image is formed in the rectangular exposure area having a longerside in the X-direction and a shorter side in the Y-direction on thewafer W. The wafer stage WS is two-dimensionally movable along the wafersurface (i.e., the XY plane) under the effect of a driving system notshown. The positional coordinates thereof are measured by aninterferometer WIF using a wafer moving mirror WM and positionallycontrolled.

FIG. 8 illustrates the positional relationship between the rectangulareffective exposure area formed on the wafer and the reference opticalaxis in second and third embodiments of the invention. In the second andthird embodiments of the invention, as shown in FIG. 8, in a circulararea (image circle) IF having a radius B around the reference opticalaxis AX as the center, the rectangular effective exposure area ER havinga desired size is set at a position eccentric by A from the referenceaxis in the −Y direction. The effective exposure area ER has anX-direction length LX and a Y-direction length LY.

In other words, in the second, and third embodiments, a rectangulareffective exposure area ER having a desired size is set at a positionapart by a off-axis amount A from the reference optical axis AX in the−Y direction, and the radius B of the circular image circle IF isregulated so as to comprehensively envelope the effective exposure areaER with the reference optical axis AX as the center. In response tothis, on the reticle R, a rectangular illuminating area (i.e., effectiveillumination area) having a size and shape corresponding to theeffective exposure area ER is formed at a position apart from thereference optical axis AX in the −Y direction by a distancecorresponding to the off-axis amount A.

FIG. 9 illustrates the positional relationship between the rectangulareffective exposure area formed on a wafer and the reference optical axisin a fourth embodiment of the present invention. In the fourthembodiment of the invention, as shown in FIG. 9, in a circular area(image circle) IF having a radius B around the reference optical axis AXas the center, a rectangular effective exposure area ER extending in along and thin shape in the X-direction is set with the reference opticalaxis as the center. The effective exposure area ER has an X-directionlength LX and a Y-direction length LY. Although not shown, therefore, inresponse to this, a rectangular illuminating area having a size andshape corresponding to the effective exposure area ER around thereference optical axis AX as the center, is formed on the reticle R.

The exposure apparatus of this embodiment has a configuration in which,from among the optical members forming the projection optical system PL,the interior of the projection optical system PL is kept in an air-tightstate between the optical member arranged at a position the closest tothe reticle (in the fourth embodiment, the lens L11) and the boundarylens Lb arranged at a position the closest to the wafer W. The gas inthe projection optical system PL is substituted by an inert gas such ashelium gas or nitrogen or kept substantially in a vacuum state. Thereticle R, the reticle stage RS and the like are arranged in a narrowoptical path between the illuminating optical system IL and theprojection optical system PL. The inert gas such as nitrogen or heliumgas is filled in the interior of a casing (not shown) hermeticallyenclosing the reticle R, the reticle stage RS and the like, or theinterior is maintained substantially in a vacuum state.

FIG. 10 schematically illustrates the configuration between the boundarylens and the wafer in the embodiments. In the individual embodiments,the boundary lens Lb arranged at a position the closest to the wafer ofthe projection optical system PL has a convex surface toward the reticle(the first face). In other words, the face Sb of the boundary lens Lb onthe reticle side has a positive refractive power. A parallel flat sheetLp is detachably inserted in the optical path between the boundary lensLb and the wafer W. The optical path between the boundary lens Lb andthe optical path between the parallel flat sheet Lp and the wafer W arefilled with a medium Lm having a refractive index larger than 1.1. Asthe medium Lm, the second and the fourth embodiments use deionizedwater, and the third embodiment uses a fluorine-based inert liquid suchas Florinat.

In order to continue filling the optical path between the boundary lensLb of the projection optical system PL and the wafer W with the liquidmedium Lm during a period from beginning to end of scanning exposure inan exposure apparatus based on the step-and-scan process whichaccomplishes scanning and exposure while moving the wafer W relative tothe projection optical system PL, for example, a technique disclosed inthe above-mentioned International Publication No. WO99/49504 or atechnique disclosed in Japanese Unexamined Patent ApplicationPublication No. 10-303114 is applicable.

The technique disclosed in the International Publication No. WO99/49504comprises the steps of filling an optical path between a boundary lensLb and a wafer W with a liquid (medium Lm) of which the temperature isadjusted to a prescribed level from a liquid feeder via a supply pipeand a discharge nozzle, and collecting the liquid from the wafer W bymeans of the liquid feeder via a collecting pipe and an inlet nozzle.The amount of supplied liquid and the amount of collected liquid areadjusted in response to the moving speed of the wafer W relative to theprojection optical system PL.

On the other hand, the technique disclosed in Japanese Unexamined PatentApplication Publication No. 10-303114 comprises the steps of using awafer holder table WT formed into a container so as to contain a liquid(medium Lm), and positioning and holding a wafer W by vacuum suction atthe center of the inner bottom (in the liquid). A configuration isadopted so that the body tube tip of the projection optical system isimmersed in the liquid and the optical face of the boundary lens Lb onthe wafer side reaches the liquid level.

An atmosphere in which the exposure light is substantially unabsorbed isprovided over the entire optical path from the light source 100 to thewafer W. As described above, the illumination area on the reticle Rregulated by the projection optical system PL and the exposure area onthe wafer W (i.e., the effective exposure area ER) are rectangular inshape having shorter sides running in the Y-direction. Therefore, areticle pattern is scanned and exposed on an area having a width equalto the longer side of the exposure area and a length corresponding tothe amount of scanning (amount of movement) of the wafer W on the waferW by synchronously moving (scanning) the reticle stage RS and the waferstage WS, i.e., the reticle R and the wafer W in the shorter-sidedirection of the rectangular exposure area and illumination area, whileperforming positional control of the reticle R and the wafer W by meansof a driving system and an interferometer (RIF, WIF).

In the embodiments, the aspherical surface is expressed by the followingequation (4) (which is equivalent to equation (3) using differentnotation) on the assumption of a height y in a direction perpendicularto the optical axis, a distance z (amount of sagging) in the opticalaxis direction between a contact plane at the apex of the asphere and aposition on the asphere at the height y, an apex radius of curvature r,a conical coefficient κ, and an n-dimensional asphere coefficient Cn. Inthe embodiments, the lens surfaces formed into aspheric shape are markedwith * to the right of the surface numbers.z=(y ² /r)/[1+{1−(1+K)·y ² /r ²}^(1/2) ]+C ₄ ·y ⁴ +C ₆ ·y ⁶ +C ₈ ·y ⁸ +C₁₀ ·y ¹⁰ +C ₁₂ ·y ¹² +C ₁₄ ·y ¹⁴ +C ₁₆ ·y ¹⁶ +C ₁₈ ·y ¹⁸ +C ₂₀ ·y²⁰  (4)

FIG. 11 illustrates the lens configuration of the projection opticalsystem of the second embodiment of the present invention. In the secondembodiment, the projection optical system PL comprises a first imageforming optical system G1 of the refraction type for forming a firstintermediate image of the pattern of a reticle arranged on the objectsurface (plane 1), a second image forming optical system G2 for forminga second intermediate image (the first intermediate image which is asecondary image of the reticle pattern) including a concave reflectorCM, and a third image forming optical system of the refraction type forforming a final image (a reduced image of the reticle pattern) of thereticle pattern on the wafer W arranged on the image field (plane 2) onthe basis of the light from the second intermediate image.

A first optical path bending mirror M1 for deflecting the light from thefirst image forming optical system G1 toward the second image formingoptical system G2 is arranged near the forming position of the firstintermediate image in the optical path between the first image formingoptical system G1 and the second image forming optical system G2. Asecond optical path bending mirror M2 for deflecting the light from thesecond image forming optical system G2 toward the third image formingoptical system G3 is arranged near the forming position of the secondintermediate image in the optical path between the second image formingoptical system G2 and the third image forming optical system G3.

The first image forming optical system G1 has a linearly extendingoptical axis AX1. The third image forming optical system G3 has alinearly extending optical axis AX3. The optical axis AX1 and theoptical axis AX3 are set so as to aligned with a reference optical axisAX which is a common single optical axis. The reference optical axis AXis positioned in the gravity direction (i.e., vertical direction). As aresult, the reticle R and the wafer W are arranged in parallel with eachother along a plane perpendicular to the gravity direction, i.e., alonga horizontal plane. In addition, all the lenses forming the first imageforming the first image forming optical system G1 and all the lensesforming the third image forming optical system G3 are arranged along thehorizontal plane on the reference optical axis AX.

On the other hand, the second image forming optical system G2 also hasan optical axis AX2 extending linearly, and this optical axis AX2 is setso as to be perpendicular to the reference optical axis AX. The firstoptical path bending mirror M1 and the second optical path bendingmirror M2 have flat reflecting faces, and are integrally formed as asingle optical member (a single optical path bending mirror) having tworeflecting faces. The line of intersection of these two reflecting faces(strictly, the line of intersection of the virtual extension surfacesthereof) are set so as to cross AX1 of the first image forming opticalsystem G1, AX2 of the second image forming optical system G2, and AX3 ofthe third image forming optical system G3 at one point.

In the second embodiment, an ArF excimer laser source is used as a lightsource 100. Quartz (SiO₂) is used for all the refracting optical members(lens components) forming the projection optical system PL and theparallel flat sheet Lp. The ArF excimer laser beam which is the exposurelight has an oscillation center wavelength of 193.306 nm, and quartz hasa refractive index of 1.5603261 for this center wavelength. Deionizedwater having a refractive index of 1.47 for the exposure light is usedas the medium Lm present between the boundary lens Lb and the wafer W.

In the projection optical system PL in the second embodiment, the firstimage forming optical system G1 comprises, sequentially from thereticles side, a positive meniscus lens L11 with a convex face thereofdirected toward the reticle; a biconvex lens L12 with an asphericalconvex surface or face thereof directed toward the wafer; a positivemeniscus lens L13 with a convex surface thereof directed toward thereticles; a positive meniscus lens L14 with a concave surface thereofdirected toward the reticle; a negative meniscus lens L15 with a concavesurface thereof directed toward the reticle; a positive meniscus lensL16 with a concave surface thereof directed toward the reticle; apositive meniscus lens L17 with an aspherical concave surface thereofdirected toward the reticle; a positive meniscus lens L18 with a concaveface thereof directed toward the reticle; a biconvex lens L19; and apositive meniscus lens L110 with an aspherical concave surface thereofdirected toward the wafer.

The second image forming optical system G2 comprises, sequentially fromthe reticle side (i.e., from the incident side) along the forwardrunning path of the light, a negative meniscus lens L21 with anaspherical concave surface thereof directed toward the reticle; anegative meniscus lens L22 with a concave surface thereof directedtoward the reticle; and a concave reflector CM.

The third image forming optical system G3 comprises, sequentially fromthe reticle side in the running direction of the light, a positivemeniscus lens L31 with a concave surface thereof directed toward thereticle; a biconvex lens L32; a positive meniscus lens L33 with anaspherical concave surface thereof directed toward the wafer; a biconvexlens L34; a positive meniscus lens L35 with an aspherical concavesurface thereof directed toward the reticle; a positive meniscus lensL36 with an aspherical concave surface thereof directed toward thewafer; an aperture stop AS; a biconvex lens L37; a negative meniscuslens L38 with a concave surface thereof directed toward the reticle; apositive meniscus lens L310 with a convex surface thereof directedtoward the reticle; a positive meniscus lens L311 with an asphericalconcave surface thereof directed toward the wafer; a positive meniscuslens L312 with a convex face thereof directed toward the reticle; and aflat-convex lens L313 (a boundary lens Lb) with a flat surface thereofdirected toward the wafer.

A parallel flat sheet Lp is arranged in the optical path between theflat-convex lens L313 serving as a boundary lens Lb and the wafer W. Theoptical path between the boundary lens Lb and the parallel flat sheetLp, and the optical path between the parallel flat sheet Lp and thewafer W are filled with a medium Lm comprising deionized water.

The following Tables 3 and 4 show various parameters of the projectionoptical system PL of the second embodiment of FIG. 11. In Table 3, λrepresents a center wavelength of the exposure light; β, a projectionmagnification (an image forming magnification for all the systems); NA,a numerical aperture on the image side (wafer side); B, a radius of animage circle IF on the wafer W; A, an off-axis amount of the effectiveexposure area ER; LX, a size (longer side size) in the X-direction ofthe effective exposure area ER; and LY, a size (shorter side size) inthe Y-direction of the effective exposure area ER.

The surface number represents the sequence from the reticle side in thelight running direction from the reticle surface which is the objectsurface (plane 1) toward the wafer surface which is the image field(plane 2); r, curvature radii of the surfaces (in the case of anaspherical face, the apex curvature radii: in mm); d, the interval onthe axis of the surfaces, i.e., the surface interval (mm); ED, theeffective diameter (mm) of each surface; n, the refractive indexrelative to the center wavelength.

The surface interval d changes the sign every time reflection occurs.The sign of the surface interval is negative in the optical path fromthe reflecting surface of the first optical bending mirror M1 to theconcave reflector CM and in the optical path extending from thereflecting surface of the second optical path bending mirror M2 to theimage field. In the other optical paths, the sign is positive. For thefirst image forming optical system G1, the radius of curvature of theconvex surface directed toward the reticle has a positive sign, and theradius of curvature of the concave surface has a negative sign. On theother hand, for the third image forming optical system G3, the radius ofcurvature toward the reticle has a positive sign, and the radius ofcurvature of the convex surface has a negative sign. For the secondimage forming optical system G2, the radius of curvature of the concaveradius toward the reticle (i.e., on the incident side) has a positivesign, and the radius of curvature of the convex surface has a negativesign. The notation in Tables 3 and 4 is used also in the next Tables 5and 6.

The following parameter values apply to Tables 3 and 4:

-   λ=193.306 nm-   β=−¼-   NA=1.0-   D=B=15 mm-   A=3 mm-   LX=26 mm-   LY=4.4 mm-   Cb=0.01095 mm⁻¹-   P=0 mm⁻¹-   Cb·D/NA=0.164-   |P·D|=0

TABLE 3 Surface No. r (mm) d (mm) n Reticle Surface 108.2689 501244.17278 32.6883 1.5603261 (L11) 502 12431.0855 40.5868 503 218.0025443.8864 1.5603261 (L12)  504* −901.16882 1 505 95.35438 40.62211.5603261 (L13) 506 255.04609 43.5025 507 −357.02117 25.9377 1.5603261(L14) 508 −305.85533 29.8146 510 −2549.65778 4.178 511 −591.6617423.2188 1.5603261 (L16) 512 −399.04534 8.7209  513* −231.3931 20.23461.5603261 (L17) 514 −148.33833 17.4652 515 −354.63058 50 1.5603261 (L18)516 −136.53902 1 517 5811.09639 34.5332 1.5603261 (L19) 518 −219.00801 1519 208.57104 29.3963 1.5603261 (L110)  520* 18419.59845 90.9569 521 ∞−244.3047 (M1)  522* 131.03687 −18.0014 1.5603261 (L21) 523 305.47877−26.1693 524 100.48802 −16.0009 1.5603261 (L22) 525 385.87639 −26.7822526 149.24479 26.7822 (CM) 527 385.87639 16.0009 1.5603261 (L22) 528100.48802 26.1693 529 305 18.0014 1.5603261 (L21)  530* 131.03687244.3047 531 ∞ −64.0489 (M2) 532 529.91109 −39.4419 1.5603261 (L31) 533219.30879 −26.0915 534 −1009.84284 −33.6721 1.5603261 (L32) 535345.39448 −1 536 −176.43124 −49.9914 1.5603261 (L33)  537* −663.25312−119.1058 538 205.20912 −14.0042 1.5603261 (L34) 539 −198.561 −115.1819 540* 1437.46317 −49.99588 1.5603261 (L35) 541 188.22741 −15.3421 542−212.79097 −49.9776 1.5603261 (L36)  43* −1223.58584 −25.593 544 ∞−1.0003 (AS) 545 −15481.75066 −23.7099 1.5603261 (L37) 546 362.44209−12.9484 547 209.8877 −14.0041 1.5603261 (L38) 548 345.03468 −1.0007 549−11942.14877 −29.1119 1.5603261 (L39) 550 278.1043 −1 551 −157.59127−26.2942 1.5603261 (L310) 552 −333.08397 −1 553 −127.00506 −33.4381.5603261 (L311)  554* −354.79236 −1.0073 555 −119.95893 −27.90941.5603261 (L312) 556 −139.80778 −1 557 −91.35661 −34.5243 1.5603261(L313:Lb) 558 ∞ −1 1.47 (Lm) 559 ∞ −4 1.5603261 (Ln) 560 ∞ −5 1.47 (Lm)Wafer surface

TABLE 4 κ C₄ Aspheric C₁₂ C₁₄ C₆ C₈ C₁₀  4 0   3.88992 × 10⁻⁸ −7.82619 ×10⁻¹³   5.12223 × 10⁻¹⁷ −2.73274 × 10⁻²¹     6.02784 × 10⁻²⁶ 0 13 0−6.25952 × 10⁻⁸   5.48030 × 10⁻¹³ −3.31838 × 10⁻¹⁶ 1.38375 × 10⁻²⁰−1.04055 × 10⁻²⁴   3.26369 × 10⁻²⁹ 20 0   1.72798 × 10⁻⁸ −1.61452 ×10⁻¹³ −4.93244 × 10⁻¹⁹ 1.04591 × 10⁻²² −1.24577 × 10⁻²⁶   6.24349 ×10⁻³¹ 22 & 30 0 −8.82578 × 10⁻⁸ −2.18452 × 10⁻¹² −8.66533 × 10⁻¹⁷−3.62594 × 10⁻²¹   −5.01578 × 10⁻²⁵   2.58145 × 10⁻²⁹ 37 0 −7.06709 ×10⁻⁹   2.17699 × 10⁻¹³   4.99998 × 10⁻¹⁸ 9.16340 × 10⁻²³   4.71865 ×10⁻²⁸ −1.92011 × 10⁻³¹ 40 0   5.99640 × 10⁻⁸ −2.38721 × 10⁻¹³ −2.67049 ×10⁻¹⁸ 8.91192 × 10⁻²² 0 0 43 0 −1.17799 × 10⁻⁸ −5.24366 × 10⁻¹³ −2.67126× 10⁻¹⁷ 1.52192 × 10⁻²¹ −2.95585 × 10⁻²⁶ 0 54 0 −5.15363 × 10⁻⁹-−2.43381 × 10⁻¹²   6.03374 × 10⁻¹⁷ 2.56676 × 10⁻²¹ −6.31540 × 10⁻²⁵  1.49243 × 10⁻²⁹

FIG. 12 illustrates lateral aberration. In the aberration diagram, Yrepresents the image height. The notation used in FIG. 12 applies alsoin the subsequent FIGS. 14 and 16. As is clear from the aberrationdiagram shown in FIG. 12, while, in the second embodiment, a very largeimage-side numerical aperture (NA=1.0) is ensured by using an ArFexcimer laser beam, the aberration is satisfactorily corrected over theentire effective exposure area.

FIG. 13 illustrates the lens configuration of the projection opticalsystem of the third embodiment of the present invention. The projectionoptical system PL of the third embodiment is areflection/refraction-type optical system having basically the sameconfiguration as in the second embodiment. In the third embodiment,however, unlike the second embodiment, an F₂ laser source is used as thelight source 100. Calcium fluoride (CaF₂) is employed for all therefractive optical members (lens components) forming the projectionoptical system PL and the parallel flat sheet Lp. F₂ laser beam servingas the exposure light has an oscillation center wavelength of 157.631nm, and for this center wavelength, the calcium fluoride has arefractive index of 1.5592267. A fluorine-based inert liquid having arefractive index of 1.36 to the exposure light is used as the medium Lmbetween the boundary lens Lb and the wafer W.

In the projection optical system PL of the third embodiment, the firstimage forming optical system G1 comprises, sequentially from the reticleside, a positive meniscus lens L11 with a convex surface thereofdirected toward the reticle; a biconvex lens L12 with an asphericalconvex surface thereof directed toward the wafer; a positive meniscuslens L13 with a convex surface thereof directed toward the reticle; apositive meniscus lens L14 with a concave surface thereof directedtoward the reticle; a negative meniscus lens 115 with a concave surfacethereof directed toward the reticle; a negative meniscus lens L16 with aconcave surface thereof directed toward the reticle; a positive meniscuslens L17 with an aspherical concave surface thereof directed toward thereticle; a positive meniscus lend L18 with a concave surface thereofdirected toward the reticle; a biconvex lens L19; and a biconvex lensL110 with an aspherical surface thereof directed toward the wafer.

The second image forming optical system G2 comprises, sequentially fromthe reticle side (i.e., from the incident side) along the running pathof light, a negative meniscus lens L21 with an aspherical concavesurface thereof directed toward the reticle; a negative meniscus lensL22 with a concave surface thereof directed toward the reticle; and aconcave reflector CM.

The third image forming optical system G3 comprises, sequentially fromthe reticle side along the running path of light, a positive meniscuslens L31 with a concave surface thereof directed toward the reticle; abiconvex lens L32; a positive meniscus lens L33 with an asphericalconcave surface thereof directed toward the wafer; a biconvex lens L34;a positive meniscus lens L35 with an aspherical concave surface thereofdirected toward the reticle; a positive meniscus lens L36 with anaspherical concave surface thereof directed toward the wafer; anaperture stop AS; a biconvex lens L37; a negative meniscus lens L38 witha concave surface thereof directed toward the reticle; a positivemeniscus lens L310 with a convex surface thereof directed toward thereticle; a positive meniscus lens L311 with an aspherical concavesurface thereof directed toward the wafer; a positive meniscus lens L312with a convex surface thereof directed toward the reticle; and a flatconvex lens L313 (boundary lens Lb) with a flat surface thereof directedtoward the wafer.

A parallel flat sheet Lp is arranged in an optical path between the flatconvex lens L313 serving as the boundary lens Lb and the wafer W. Anoptical path between the boundary lens Lb and the parallel flat sheet Lpand an optical path between the parallel flat sheet Lp and the wafer Ware filled with a medium Lm comprising a fluorine-based inert liquid. Inthe third embodiment, in which a relatively large light quantity lossoccurs upon passing through the medium Lm comprising the fluorine-basedinert liquid, the distance between the parallel flat sheet Lp and thewafer W, i.e., the working distance, is set to a value considerablysmaller than in the first embodiment. The following Tables 5 and 6 showvarious parameters of the projection optical system PL of the thirdembodiment. The following parameter values apply in Tables 5 and 6:

-   λ=157.631 nm-   β=−¼-   NA=1.0-   D=B=15 mm-   A=3 mm-   LX=26 mm-   LY=4.4 mm-   Cb=0.01087 mm¹-   P=0 mm⁻¹-   Cb·D/NA=0.163-   |P·D|=0

TABLE 5 Surface No. r (mm) d (mm) n Reticle surface 101.913 501225.91181 34.4965 1.5592267 (L11) 502 1436.06203 33.7438 503 201.9122549.2729 1.5592267 (L12)  504* −841.64457 1 505 96.6787 38.2983 1.5592267(L13) 506 257.84523 43.1608 507 −380.28084 27.546 1.5592267 (L14) 508−312.16425 30.1639 509 −124.06734 28.9267 1.5592267 (L15) 510 −557.961513.8304 511 −366.97659 22.7734 1.5592267 (L16) 512 −456.35163 12.9347 513* −254.00244 19.0622 1.5592267 (L17) 514 −156.7197 14.5386 515−336.79481 46.8839 1.5592267 (L18) 516 −133.2981 2.8796 517 2442.5587949.687 1.5592267 (L19) 518 −237.47884 1.195 519 210.34651 30.77541.5592267 (L110)  520* −18494.54411 86.6055 521 ∞ −256.5916 (M1)  522*137.75129 −18 1.5592267 (L21) 523 355.77715 −27.9942 524 100.61796 −161.5592267 (L22) 525 376.58992 −26.125 526 150.70332 26.125 (CM) 527376.58992 16 1.5592267 (L22) 528 100.61796 27.9942 529 355.77715 181.5592267 (L21)  530* 137.75129 256.5916 531 ∞ −64.0489 (M2) 532529.4817 −37.2168 1.5592267 (L31) 533 217.84933 −45.5764 534 −906.17992−39.8472 1.5592267 (L32) 535 390.17706 −1 536 −175.866 −49.69871.5592267 (L33)  537* −666.25803 −123.631 538 193.90829 −14.4511.5592267 (L34) 539 −194.01757 −115.5693  540* 1756.45056 −49.99921.5592267 (L35) 541 192.14442 −16.6644 542 −212.68601 −46.8499 1.5592267(L36)  543* −1313.55988 −26.5088 544 ∞ −1 (AS) 545 −46713.1214 −22.71231.5592267 (L37) 546 380.61069 −13.0721 547 213.48092 −14.0147 1.5592267(L38) 548 358.25443 −1 549 −3283.23016 −29.4719 1.5592267 (L39) 550287.34852 −1 551 −177.16315 −23.5067 1.5592267 (L310) 552 −351.98397 −1553 −121.82696 −35.6149 1.5592267 (L311)  554* −392.8455 −1 555 −117.938−28.2524 1.5592267 (L312) 556 −138.49028 −1 557 −91.96471 −39.691.5592267 (L313:Lb) 558 ∞ −1 1.36 (Lm) 559 ∞ −4 1.5592267 (Ln) 560 ∞ −11.36 (Lm) Wafer surface

TABLE 6 κ C₄ Aspheric C₁₂ C₁₄ C₆ C₈ C₁₀  4 0 −4.99618 × 10⁻⁸ −7.39398 ×10⁻¹³   6.16730 × 10⁻¹⁷ −3.94177 × 10⁻²¹     8.18197 × 10⁻²⁶ 0 13 0−6.25952 × 10⁻⁸   1.42305 × 10⁻¹² −2.81530 × 10⁻¹⁶ 1.39566 × 10⁻²⁰−5.93253 × 10⁻²⁵   1.35088 × 10⁻²⁹ 20 0   1.68383 × 10⁻⁸ −1.06688 ×10⁻¹³ −2.92682 × 10⁻¹⁸ 2.12089 × 10⁻²² −1.38926 × 10⁻²⁶   5.21818 ×10⁻³¹ 22 and 30 0 −8.30158 × 10⁻⁸ −1.66607 × 10⁻¹² −6.51740 × 10⁻¹⁷−4.60984 × 10⁻²¹   −7.40500 × 10⁻²⁶ −9.34635 × 10⁻³⁰ 37 0 −5.68895 ×10⁻⁹   2.19286 × 10⁻¹³   5.12916 × 10⁻¹⁸ 6.51778 × 10⁻²³ −5.40821 ×10⁻²⁹ −2.41357 × 10⁻³¹ 40 0   5.94153 × 10⁻⁸ −2.72431 × 10⁻¹³ −3.72411 ×10⁻¹⁸ 8.85563 × 10⁻²² 0 0 43 0 −1.10623 × 10⁻⁸ −5.34092 × 10⁻¹³ −2.58209× 10⁻¹⁷ 1.51679 × 10⁻²¹ −3.00290 × 10⁻²⁶ 0 54 0 −5.82309 × 10⁻⁹ −2.25140× 10⁻¹²   6.80911 × 10⁻¹⁷ 3.12945 × 10⁻²¹ −7.25627 × 10⁻²⁵   2.57401 ×10⁻²⁹

FIG. 14 illustrates the lateral aberration in the third embodiment. Asis evident from the aberration diagram shown in FIG. 14, in the thirdembodiment, while a very large image-side numerical aperture (NA=1.0) iskept, the aberration is satisfactorily corrected over the entireeffective exposure area.

FIG. 15 illustrates the lens configuration of the projection opticalsystem of a fourth embodiment of the present invention. The projectionoptical system PL is a refraction-type optical system, unlike the first,second and third embodiments. However, in the fourth embodiment, as inthe second embodiment, an ArF excimer laser source is used as the lightsource 100, and deionized water having a refractive index of 1.47relative to the exposure light is used as the medium Lm provided betweenthe boundary lens Lb and the wafer W.

In the fourth embodiment, quartz (SiO₂) or calcium fluoride (CaF₂) isused for the refractive optical member (a lens component) and theparallel flat sheet Lp forming the projection optical system PL. Morespecifically, lenses L13, L17, L18, L114, L115, L122 and L123 (Lb) areformed from calcium fluoride, and the other lenses and the parallel flatsheet Lp are formed from quartz. The ArF excimer laser beam serving asthe exposure light has an oscillation center wavelength of 193.306 nm.Quartz has a refractive index of 1.5603261 for this center wavelength,and calcium fluoride has a refractive index of 1.5014548.

The projection optical system PL of the fourth embodiment comprises,sequentially from the reticle side, a biconcave lens L11 with anaspherical concave surface thereof directed toward the wafer; a negativemeniscus lens L12 with a concave surface thereof directed toward thereticle; a positive meniscus lens L13 with a concave surface thereofdirected toward the reticle; a positive meniscus lens L14 with anaspherical concave surface thereof directed toward the reticle; apositive meniscus lens L16 with a convex surface thereof directed towardthe reticle; a positive meniscus lens L17 with a convex surface thereofdirected toward the reticle; a positive meniscus lens L18 with a convexsurface thereof directed toward the reticle; a negative meniscus lensL19 with a convex surface thereof directed toward the reticle; abiconcave lens L110 with an aspherical concave surface thereof directedtoward the reticle; a biconcave lens L111 with an aspherical concavesurface thereof directed toward the wafer; a biconcave lens L112 with anaspherical concave surface thereof directed toward the wafer; a positivemeniscus lens L113 with an aspherical concave surface thereof directedtoward the wafer; a biconvex lens L114; a biconvex lens L115; a negativemeniscus lens L116 with a convex surface thereof directed toward thereticle; an aperture stop AS; a biconcave lens L117; a positive meniscuslens L118 with a concave surface thereof directed toward the reticle; abiconvex lens L119; a positive meniscus lens L120 with a convex surfacethereof directed toward the reticle; a positive meniscus lens L121 withan aspherical concave surface thereof directed toward the wafer; apositive meniscus lens L122 with a convex surface thereof directedtoward the reticle; and a negative meniscus lens L123 (boundary lens Lb)with a convex surface thereof directed toward the reticle.

A parallel flat sheet Lp is arranged in an optical path between thenegative meniscus lens L123 serving as a boundary lens Lb and the waferW. An optical path between the boundary lens Lb and the parallel flatsheet Lp and an optical path between the parallel flat sheet Lp and thewafer W are filled with a medium Lm comprising deionized water.

The following Tables 7 and 8 show parameters of the projection opticalsystem PL of the fourth embodiment. In Table 7 and 8, λ represents thecenter wavelength of the exposure light; β, a projection magnification(image forming magnification for the entire system); NA, the numericalaperture on the image side (wafer side); B, the radius of an imagecircle on the wafer W; LX, the size (the size of the longer side) of theeffective exposure area ER in the X-direction; and LY, the size (thesize of the shorter side) of the effective exposure area ER in theY-direction.

The surface number represents the sequence of a surface from the reticleside in the light running direction from the reticle surface which isthe object surface (surface 1) to the wafer surface which is the imagefield (surface 2); r represents the radius of curvature of each surface(apex radius of curvature in the case of an aspherical surface: in mm);d, the interval on the axis of each surface, i.e., the surface interval(mn); ED, the effective diameter (mm) of each surface; and n, therefractive index for a center wavelength. It is assumed that the radiusof curvature of a convex surface directed toward the reticle ispositive, and a concave surface has a negative radius of curvature. Thefollowing parameter values apply in Tables 7 and 8:

-   λ=193.306 nm-   β=−¼-   NA=0.9-   D=B=12 mm-   LX=22 mm-   LY=9 mm-   Cb=0.002 mm⁻¹-   P=0 mm⁻¹-   Cb·D/NA=0.0267-   |P·D|=0

TABLE 7 Surface No. r (mm) d (mm) n (Reticle face) 55.8515 501−2113.36467 22.0016 1.5603261 (L11)  502* 216.83131 37.6588 503 −9935.9329 1.5603261 (L12) 504 −530.65397 1 505 −2085.24301 49.68841.501548 (L13) 506 −211.94203 1  507* −1300.49159 51 1.5603261 (L14) 508−228.7234 1 509 449.54298 42.9915 1.5603261 (L15) 510 −31743139.734.4564 511 286.16093 46.424 1.5603261 (L16) 512 700 27.3629 514835.17809 1 515 176.47058 44.0153 1.5014548 (L18) 516 4997.43477 1 5171190.04003 14.0931 1.5603261 (L19) 518 117.90394 42.896  519* −174.9998714 1.5603261 (L110) 520 122.55049 22.0064 521 −9702.06368 10 1.5603261(L111)  522* 501.0497 22.5348 523 −150 15.2478 1.5603261 (L112)  524*545.44066 5.0208 525 670.66815 37.0463 1.5603261 (L113)  526* 1258.716619.9406 527 5070.2394 51.1959 1.5014548 (L114) 528 −161.64547 1 529827.78244 41.9662 1.5014548 (L115) 530 −354.18335 2.2506 531 4796.1016621.3348 1.5603261 (L116) 532 2003.44485 100.6473 534 ∞ 19.4869 (AS) 534−1507.37025 26.9184 1.5603261 (L117) 535 1249.53353 17.3121 536−3874.77086 48.5508 1.5603261 (L118) 537 −333.94853 1 538 1503.9389441.7658 1.5603261 (L119) 539 −563.59244 1 540 186 57.7875 1.5603261(L120) 541 997.61736 1 542 158.43716 36.3731 1.5603261 (L121)  543*202.36197 1 544 120 48.8077 1.5014548 (L122) 545 244.45698 7.8937 546500 45.5175 1.5014548 (L123:Lb) 547 100.78932 4.5 1.47 (Lm) 548 ∞ 41.5603261 (Lp) 549 ∞ 9 1.47 (Lm) 550 551 −177.16315 −23.5067 1.5592267(L310) 552 −351.98397 −1 553 −121.82696 −35.6149 1.5592267 (L311)  554*−392.8455 −1 555 −117.938 −28.2524 1.5592267 (L312) 556 −138.49028 −1557 −91.96471 −39.69 1.5592267 (L313:Lb) 558 ∞ −1 1.36 (Lm) 559 ∞ −41.5592267 (Ln) 560 ∞ −1 1.36 (Lm) Wafer

TABLE 8 κ C₄ Aspheric C₁₂ C₁₄ C₆ C₈ C₁₀ 2 0 −1.49703 × 10⁻⁷ 6.71854 ×10⁻¹² −3.64562 × 10⁻¹⁶ 4.13593 × 10⁻²⁰ −2.03062 × 10⁻²⁴   5.69043 ×10⁻²⁹ 7 0 −1.18880 × 10⁻⁸ 1.02901 × 10⁻¹³ −7.54528 × 10⁻¹⁹ 5.83141 ×10⁻²³   1.74725 × 10⁻²⁸ −4.32881 × 10⁻³² 19 0 −7.74045 × 10⁻⁸ 1.56057 ×10⁻¹¹ −1.10312 × 10⁻¹⁵ 3.62488 × 10⁻²⁰   3.26842 × 10⁻²⁴ −3.56309 ×10⁻²⁸ 22 0 −1.04821 × 10⁻⁷ 8.80831 × 10⁻¹²   3.69747 × 10⁻¹⁷ −2.96855 ×10⁻²⁰   −4.51996 × 10⁻²⁴   4.81943 × 10⁻²⁸ 24 0   1.27905 × 10⁻⁸ 7.05643× 10⁻¹³ −4.87282 × 10⁻¹⁶ 4.68907 × 10⁻²⁰ −8.61747 × 10⁻²⁵ −7.01397 ×10⁻²⁹ 26 0   7.26173 × 10⁻⁸ −3.04123 × 10⁻¹²   −2.32724 × 10⁻¹⁷ 8.20189× 10⁻²¹ −4.70258 × 10⁻²⁵   1.17373 × 10⁻²⁹ 43 0 −1.90186 × 10⁻⁸ −8.61256× 10⁻¹⁴     1.45348 × 10⁻¹⁷ 4.84634 × 10⁻²⁴   3.04007 × 10⁻²⁷   4.59309× 10⁻³¹

FIG. 16 illustrates a lateral aberration in the fourth embodiment. As isclear from the aberration diagram shown in FIG. 16, in the fourthembodiment, while a relatively large image-side numerical aperture(NA=0.9) is maintained by using an ArF excimer laser beam in therefraction-type projection optical system, the aberration issatisfactorily corrected over the entire effective exposure area.

Thus, in the second embodiment, it is possible to ensure a highimage-side numerical aperture of 1.0 for the ArF excimer laser beamhaving a wavelength of 193.306 nm and maintain a rectangular effectiveexposure area (stationary exposure area) having a size of 26 mm×4.4 mmas an area in which various aberrations are sufficiently correctedwithin an image circle having a radius of 15 mm on the wafer W. Forexample, a circuit pattern can be scanned and exposed at a highresolution within a 26 mm×33 mm rectangular exposure area.

In the third embodiment, it is possible to ensure a high image-sidenumerical aperture of 1.0 for the F₂ laser beam having a wavelength of157.631 nm and maintain a rectangular effective exposure area(stationary exposure area) having a size of 26 mm×4.4 mm as an area inwhich various aberrations are sufficiently corrected within an imagecircle having a radius of 15 mm on the wafer W. For example, a circuitpattern can be scanned and exposed at a high resolution within a 26mm×33 mm rectangular exposure area.

In the fourth embodiment, it is possible to ensure a high image-sidenumerical aperture of 0.9 for the ArF excimer laser beam having awavelength of 193.306 nm and maintain a rectangular effective exposurearea (stationary exposure area) having a size of 22 mm×9 mm as an areain which various aberrations are sufficiently corrected within an imagecircle having a radius of 12 mm on the wafer W. For example, a circuitpattern can be scanned and exposed at a high resolution within a 22mm×33 mm rectangular exposure area.

While, in the second embodiment, all the lens components are made ofquartz, the risk of deterioration of the image forming function causedby the compaction of quartz can be avoided by forming small-diameterlenses from calcium fluoride, on which the energy of exposure lightconcentrates (such as the boundary lens Lb arranged near the wafer W orthe lens L312).

If it is preferable to limit the condition relating to the magnificationof the third imaging lens group, the conditional expression can belimited as follows:0.75<MA/MG3<1.1  (5)

preferably 0.8<MA/MG3<1.05

where MA denotes a magnification of the whole optical system, and MG3denotes a magnification of the third imaging lens system G3.

When a numerical aperture NA for light entering to the plane mirrorhaving the role of separating optical paths becomes large, it becomesdifficult to separate optical paths, so that it becomes necessary thatthe distance between the optical axis and the exposure area is made tobe large. In order to secure sufficient exposure area, it is inevitablethat the optical system becomes large. Even if a large numericalaperture NA is expected on the image side, by satisfying a conditionalexpression regarding the magnification of the third imaging lens group,the increase in numerical aperture on entering the plane mirror isgentle, so that optical path separation can be made easier. Accordingly,a large numerical aperture NA on the image side is secured and goodoptical performance can be obtained without causing the optical systemto become large.

In order to make the numerical aperture NA large and to prevent thediameter of lenses locating in the vicinity of the aperture stop gettinglarger, it is necessary to shorten the distance between the aperturestop and the image plane (second plane) as well as to increase thecomposite positive refractive power of the focusing lens group arrangedbetween the aperture stop and the image plane. At the same time, inorder to prevent lens deformation caused by holding a lens element, itis necessary to secure sufficient edge thickness of a lens, so that itis preferable that the focusing lens group is composed of five lenselements or less. Moreover, in order to increase positive refractivepower effectively, it is preferable that the focusing lens group doesnot include a negative lens element.

For reference purposes, the following summarises the overallmagnification MA and the magnification MG3, of the third stage G3 invarious embodiments.

Magnification MA MG3 MA/MG3 1^(st) Embodiment 1/4 1/3.55 0.888 2^(nd)Embodiment(ArF) 1/4 1/3.53 0.883 3^(rd) Embodiment(F₂) 1/4 1/3.78 0.9455^(th) Embodiment 1/4 1/3.42 0.855

Tables 9 and 10 show various values associated with the fifthembodiment.

The following parameters apply in the fifth embodiment shown in FIG. 19:

NA (image side): 1.25

Magnification MA: ¼

Exposure area: A=3.5 mm, B=15.1 mm →rectangular area 26 mm×4 mm

Central Wavelength: 193.306 nm

Refractive index of silica glass: 1.5603261

Refractive index of purified water: 1.4368163

Dispersion of silica glass (dn/dλ): −1.591E-6/pm

Dispersion of purified water (dn/dλ): −2.096E-6/pm

In the meantime one example of the immersion liquid for thephotolithography machine using F₂ laser is perfluoropolyether (PFPE).

In the projection optical system PL in the fifth embodiment of FIG. 19,the first image forming optical system G1 comprises, sequentially fromthe reticle side, a positive lens L11 with a convex surface thereofdirected toward the reticle; a positive meniscus lens L12 with a convexsurface thereof directed toward the reticle; a biconvex lens L13 withwafer side aspheric surface; a positive meniscus lens L14 with a convexsurface thereof directed toward the reticle; a positive meniscus lensL15 with a concave surface thereof directed toward the reticle; anegative meniscus lens L16 with a concave surface thereof directedtoward the reticle; a positive meniscus lens L17 with concave surfacethereof directed toward the reticle; a positive meniscus lens L18 withaspheric concave surface thereof directed toward the reticle; a positivelens L19; and a positive meniscus lens L110 with aspheric surfacethereof directed toward the wafer.

The second image forming optical system G2 comprises, sequentially fromthe reticle side (i.e., from the incident side) along the forwardrunning path of the light, a negative meniscus lens L21 with anaspherical concave surface thereof directed toward the reticle; anegative meniscus lens L22 with a concave surface thereof directedtoward the reticle; and a concave reflector CM.

The third image forming optical system G3 comprises, sequentially fromthe reticle side in the running direction of the light, a positivemeniscus lens L31 with a concave surface thereof directed toward thereticle; a biconvex lens L32; a positive lens L33; a positive meniscuslens L34 with an aspherical concave surface thereof directed toward thewafer; a biconcave negative lens L35 with an aspherical concave surfacethereof directed toward the wafer; a negative meniscus lens L36 with anaspherical concave surface thereof directed toward the wafer; a biconvexlens L37; a positive lens L38 with an aspherical surface thereofdirected toward the reticle; a positive meniscus lens L39 with a convexsurface thereof directed toward the reticle; a positive lens L310 withan aspherical surface thereof directed toward the wafer; an aperturestop AS; a biconvex lens L311; a positive lens L312; a positive meniscuslens L313 with a concave aspheric surface thereof directed toward thewafer; a positive meniscus lens L314 with a concave aspheric surfacethereof directed toward the wafer; and a flat-convex lens L315 (aboundary lens Lb) with a flat face thereof directed toward the wafer.

As is apparent from FIG. 20, the fifth embodiment achieves excellentcorrection for chromatic aberration within wavelength scope of ±0.4 pm.

TABLE 9 Surface No. r (mm) d (mm) Material Object Plane ∞ 81.9091 601:2634.49417 21.2504 fused silica 602: −395.77168 1.0000 603: 150.0000050.0000 fused silica 604: 369.68733 54.9152 605: 179.71446 34.0868 fusedsilica 606: ASP-1 6.6932 607: 88.93816 50.0000 fused silica 608:91.86919 23.6059 609: −98.63242 50.0000 fused silica 610: −88.5069312.0495 611: −76.47008 38.6573 fused silica 612: −344.46033 15.7028 613:−334.92667 50.0661 fused silica 614: −117.23873 1.0000 615: ASP-243.8716 fused silica 616: −181.49712 1.0000 617: 289.19628 27.8483 fusedsilica 618: 5892.12201 12.1517 619: 227.01362 27.1570 fused silica 620:ASP-3 69.0000 621: ∞ −236.5116 (M1) 622: ASP-4 −12.5000 fused silica623: 1144.45984 −50.1326 624: 110.85976 −12.5000 fused silica 625:213.24820 −26.1588 626: 155.15866 26.1588 (CM) 627: 213.24820 12.5000fused silica 628: 110.85976 50.1326 629: 1144.45984 12.5000 fused silica630: ASP-4 236.5116 631: ∞ −64.0489 (M2) 632: 3037.95158 −22.3312 fusedsilica 633: 259.31045 −1.0000 634: −470.92323 −24.5450 fused silica 635:700.75092 −1.0000 636: −228.28898 −45.9798 fused silica 637: −4362.49907−1.0000 638: −147.00156 −50.0000 fused silica 639: ASP-5 −13.1758 640:810.59426 −12.5000 fused silica 641: ASP-6 −40.9252 642: −2113.41076−12.5000 fused silica 643: ASP-7 −16.1803 644: −562.31334 −30.6877 fusedsilica 645: 1126.64825 −80.2339 646: ASP-8 −22.6585 fused silica 647:586.42327 −1.0000 648: −361.03935 −33.1534 fused silica 649: −3170.02757−1.0000 650: −310.02927 −49.2493 fused silica 651: ASP-9 −9.8682 652: ∞−5.3722 Aperture Stop 653: −777.31707 −35.8824 fused silica 654:1312.61222 −1.0007 655: −319.73575 −35.9439 fused silica 656: 3225.49072−1.0000 657: −130.49530 −28.4950 fused silica 658: ASP-10 −1.0000 659:−95.22134 −34.3036 fused silica 660: ASP-11 −1.0000 661: −61.85167−50.0000 fused silica 662: ∞ −1.0000 deionized water image plane ∞

TABLE 10 Aspheric Curvature K A B C D No. (CURV) E F G H J ASP-1−0.00209291 0  7.81812 × 10⁻⁸   6.03387 × 10⁻¹³   3.16794 × 10⁻¹⁶−3.45599 × 10⁻²⁰   1.67268 × 10⁻²⁴ 0 0 0 0 ASP-2 −0.00252981 0 −1.14607× 10⁻⁰⁸   4.60861 × 10⁻¹³ −1.61766 × 10⁻¹⁷ −5.41414 × 10⁻²⁴   5.36076 ×10⁻²⁷ −1.16131 × 10⁻³¹ 0 0 0 ASP-3 0.00029038 0   1.29530 × 10⁻⁰⁸  2.79320 × 10⁻¹³ −1.95862 × 10⁻¹⁷   6.49032 × 10⁻²² −1.02409 × 10⁻²⁶−4.06450 × 10⁻³² 0 0 0 ASP-4 0.00934352 0 −8.88014 × 10⁻⁰⁸ −3.40911 ×10⁻¹² −1.98985 × 10⁻¹⁶ −1.45801 × 10⁻²⁰ −9.23066 × 10⁻²⁶ −1.30730 ×10⁻²⁸ 0 0 0 ASP-5 −0.00197848 0 −3.21829 × 10⁻⁰⁸   4.08976 × 10⁻¹³  9.46190 × 10⁻¹⁷ −1.12686 × 10⁻²⁰   1.09349 × 10⁻²⁴ −2.30304 × 10⁻²⁹ 00 0 ASP-6 −0.0104007 0 −1.40846 × 10⁻⁰⁸   3.73235 × 10⁻¹²   5.78170 ×10⁻¹⁷   4.02044 × 10⁻²⁰   1.81116 × 10⁻²⁴ −3.46502 × 10⁻²⁸ 0 0 0 ASP-7−0.00689746 0   3.76564 × 10⁻⁰⁸   2.04565 × 10⁻¹²   6.72661 × 10⁻¹⁷  3.35779 × 10⁻²¹ −5.51576 × 10⁻²⁵   2.95829 × 10⁻²⁸ 0 0 0 ASP-8−0.00029365 0   1.54429 × 10⁻⁰⁸ −1.52631 × 10⁻¹³ −1.17235 × 10⁻¹⁷−3.02626 × 10⁻²² −2.05070 × 10⁻²⁸   3.61487 × 10⁻³¹ 0 0 0 ASP-90.00123523 0 −9.78469 × 10⁻⁰⁹   2.15545 × 10⁻¹⁴ −2.66488 × 10⁻¹⁷  1.19902 × 10⁻²¹ −2.50321 × 10⁻²⁶   2.10016 × 10⁻³¹ 0 0 0 ASP-10−0.00508157 0   2.76215 × 10⁻⁰⁹ −4.06793 × 10⁻¹²   4.51389 × 10⁻¹⁶−5.07074 × 10⁻²⁰   1.83976 × 10⁻²⁴ −6.22513 × 10⁻²⁹ 0 0 0 ASP-11−0.00460959 0 −1.08228 × 10⁻⁰⁷ −9.51194 × 10⁻¹²   1.14605 × 10⁻¹⁵−1.27400 × 10⁻¹⁹   1.59438 × 10⁻²³ −5.73173 × 10⁻²⁸ 0 0 0

The exposure apparatus in the above-mentioned embodiments makes itpossible to manufacture microdevices (such as semiconductor devices,image pickup devices, liquid crystal display devices and thin-filmmagnetic heads) by illuminating a reticle (mask) by an illuminatingapparatus (illuminating step), and exposing a pattern for transferformed on the mask onto a photosensitive substrate by means of aprojection optical system. A typical technique for obtaining asemiconductor device as a microdevice by forming a prescribed circuitpattern on a photosensitive substrate such as a wafer by using theexposure apparatus of this embodiment will be described with referenceto a flowchart shown in FIG. 17.

In step 301 shown in FIG. 17, metal films are vapor-deposited ontowafers of one batch. In the next step 302, photoresist is coated ontothese metal films on the wafers of the batch. Subsequently in step 303,the pattern images on the masks are sequentially exposed and transferredin the individual shot areas on the wafers of the batch by using theexposure apparatus of this embodiment. Thereafter, after development ofthe photoresist on the wafers of the batch in step 304, circuit patternscorresponding to the patterns on the masks are formed in the individualshot areas on the wafers by conducting etching with the resist patternsas masks on the wafers of the batch.

Then, a device such as a semiconductor device is manufactured by formingthe circuit pattern of an upper layer. According to the above-mentionedsemiconductor device manufacturing method, a semiconductor device havinga very fine circuit pattern can be obtained at a high throughput. Insteps 301 to 305, a metal is vapor-deposited on the wafer; a resist iscoated onto the metal film; and exposure, development and etching stepsare performed. Prior to performing these steps, after forming a siliconoxide film on the wafer, resist may be coated onto the silicon oxidefilm, followed by exposure, development and etching steps.

According to the exposure apparatus of this embodiment, it is possibleto obtain a liquid crystal display device as a microdevice by forming aprescribed pattern (a circuit pattern, an electrode pattern or the like)on a plate (glass substrate). A typical technique applied at this stagewill be described with reference to the flowchart shown in FIG. 12. InFIG. 18, in the pattern forming step 401, a photolithographic step isexecuted through transfer and exposure of the pattern of the mask ontothe photosensitive substrate (a glass substrate having a resist coatedthereon, or the like) by using the exposure apparatus of thisembodiment. As a result of this photolithographic process, manyprescribed patterns including electrodes and the like are formed on thephotosensitive substrate. The prescribed patterns are formed on theexposed substrate through steps such as developing, etching and resiststripping steps, and the process advances to the next color filterforming step 402.

Then, in the color filter forming step 402, many sets of these kinds ofdots including R (red), G (green) and B (blue) are arranged in a matrixshape, or a plurality of sets of stripe filters of R, G and B arearranged in the horizontal scanning lines, to form a color filter. Afterthe color filter forming step 402, a cell assembling step 403 isexecuted. In the cell assembling step 403, a liquid crystal panel(liquid crystal cell) is assembled by using the substrate havingprescribed patterns resulting from the pattern forming step 401, and thecolor filter obtained in the color filter forming step 402. In the cellassembling step 403, a liquid crystal is injected into the spacebetween, for example, the substrate having the prescribed patternsresulting from the pattern forming step 401 and the color filterobtained in the color filter forming step 402, to manufacture a liquidcrystal panel (liquid crystal cell).

Subsequently, in a module assembling step 404, component parts such asan electric circuit causing the assembled liquid crystal panel (liquidcrystal cell) and backlights are attached, thus completing a liquidcrystal display device. According to the above-mentioned manufacturingmethod of liquid crystal display devices, it is possible to obtain aliquid crystal display device having very fine circuit patterns at ahigh throughput.

In the aforementioned embodiments, the present invention is applied tothe exposure apparatus based on the step-and-scan process in which amask pattern is scanned and exposed to exposure areas of the substratewhile moving the mask and substrate relative to the projection opticalsystem. The present invention is not however limited to this, but isapplicable also to an exposure apparatus of the step-and-repeat processin which the mask pattern is transferred in a lump onto the substrate ina stationary state of the mask and the substrate, and the mask patternsare sequentially exposed onto the exposure areas by successively movingthe substrate stepwise.

In the aforementioned embodiments, an ArF excimer laser source or an F₂laser source is used. The present invention is not however limited tothis, but other appropriate light source may be employed. The presentinvention is applied in the aforementioned embodiments to a projectionoptical system mounted on an exposure apparatus. While the presentinvention is applied to a projection optical system mounted on anexposure apparatus, the present invention is not limited to this, but isapplicable also to other popularly used projection optical systems.

According to the projection optical of the present invention, asdescribed above, occurrence of reflection loss on an optical face can besatisfactorily inhibited, and a large effective image-side numericalaperture can be maintained by providing a medium having a highrefractive index in the optical path to the image field, and imparting apositive refractive power onto the face of the boundary lens on theobject side.

Therefore, in the exposure apparatus and the exposing method using theprojection optical system of the present invention, a fine pattern canbe transferred and exposed at a high accuracy via the projection opticalsystem having a large and effective image-side numerical aperture and ahigh resolution. A satisfactory microdevice through high-accuracyprojection and exposure via a high-resolution projection optical systemby using an exposure apparatus mounting the projection optical system ofthe present invention.

1. A projection lens of a microlithographic projection exposureapparatus, comprising: a final lens element arranged as a most imagewiselens element among lenses of the projection lens, the final lens elementbeing a last lens element that light passes through before irradiatingan image plane; and a terminating element having no overall refractivepower that is positioned between, but spaced apart from, the final lenselement and the image plane of the projection lens, wherein the finallens element is adjustable, and an interspace formed between the finallens element and the terminating element is at least partly filled witha liquid and the terminating element is disposed in an optical pathbetween the final lens element and the image plane.
 2. The projectionlens according to claim 1, wherein the terminating element is aplane-parallel plate.
 3. A microlithographic projection exposureapparatus, comprising: an illumination system for generating projectionlight; and the projection lens of claim 1, wherein the terminatingelement is immersed in an immersion medium.
 4. The apparatus accordingto claim 3, wherein the terminating element is a plane-parallel plate.5. The apparatus according to claim 3, wherein the immersion medium isliquid.